The Measurement of Attitude
Chapter 1: Theory of Attitude Measurement
L. L. Thurstone and E. J. Chave
THE OBJECTIVE DESCRIPTION OF ATTITUDE
The scientific study of social phenomena suffers from the serious handicap that the phenomena that we call social are exceedingly difficult to describe in objective terms, to say nothing of quantitative measurement. Whenever objective or quantitative treatment is attempted we not infrequently feel that the very essence has been squeezed out of the effects that we want to study. About this feeling concerning quantitative treatment in the social studies two comments may be made. In the first place, when we find those aspects of a social phenomenon which lend themselves to objective and simple counting, it frequently does happen that these things that can be counted are really not essential aspects of the social phenomenon under consideration. But, further, there is also the possibility that as soon as some intriguing problem of social conduct becomes accessible to measurement we are inclined to turn our attention away as though elsewhere must reside the essence of that which we regard as vital, human, or important. This is really a bad habit.
Since the application of psychophysical methods to the measurement of social attitudes contains a certain degree of novelty, it may be appropriate to review briefly the setting in which the present experiments have grown. The psychophysical methods were developed primarily for the purpose of measuring discriminatory powers with special regard to simple sensory stimuli. The classical psychophysical experiments were devoted to the measurement of the subject's power to discriminate between lines of slightly different length, between slightly different weights that he lifted, between pairs of gray papers that differed slightly in bright-
( 2) -ness, and so on. In experiments of this kind were discovered Weber's law and Fechner's law.
Cattell seems to be the first to have extended the psychophysical methods to stimuli other than simple sensory values. He applied the psychophysical procedures with some variations to the measurement of estimated degrees of eminence of scientific men. Here, for the first time, the methods were used on stimuli which do not have any simple stimulus magnitude. When the methods are used on lifted weights, line lengths, and brightnesses, the experiments yield two scales. One is a scale of physical stimulus magnitude such as the actual weight in grams, the length of the lines in centimeters, or the photometrically determined brightness of the gray papers. It is known in psychophysics as the R-scale. The second scale is the psychological continuum, which is known as the S-scale. Its unit is the equally often noticed stimulus difference. Fechner's law describes the logarithmic relation between these two scales. Weber's law describes the average error of perception as a constant fraction of the physical stimulus magnitude. When Cattell extended the use of these methods to social stimuli he constructed, in effect, a psychological scale, the unit of measurement for which was the equally often noticed difference or some approximation to it.
But when the methods are used for measuring social values there is no simple physical stimulus value to be measured such as line length or weight. The validity of the psychological scale of equally often noticed differences must be established by other criteria of internal consistency. Cattell's students have applied the same methods with variations and short cuts to the measurement of other social values, examples of which are the experiments of Wells in measuring literary merit and the experiments of Thorndike in measuring the estimated excellence of handwriting and of children's drawings. The idea underlying such measurement is the equally often noticed difference, properly defined, as a unit of measurement. In all of these measurements, however,
( 3) there is no simple physical stimulus scale with which to match the psychological scale. Hence in these experiments the verification of Fechner's law is not an issue.
The last twenty years have witnessed a most peculiar separation into two groups of the men primarily interested in psychological measurement. One of these groups concern themselves with traditional psychophysics with primary emphasis on simple sensory stimuli. They are the psychophysicists. They have developed the psychophysical methods with considerable refinement, inspired by an interest in psychological measurement theory. The other group has proceeded with the construction of educational scales with little or no interest in the available psychophysical methods or their underlying theory. As a consequence there is at present a wide but artificial break between the group of men who work in psychophysics with the traditional stimuli and those who attempt to measure educational and social values with little interest in psychophysical theory. The present study is one of a series of experiments intended to continue the work of Cattell in applying the psychophysical methods to the measurement of social values. It is our hope again to unify the efforts to measure social values with the advancement in psychophysical theory.
We have used the method of equal-appearing intervals for the construction of our scale of attitude. There is some question about the validity of this method since the scale so produced may not be entirely consistent with the scale that would be produced by the method of paired comparison or Cattell's order of merit (rank order) procedure. We leave it for separate experimentation, however, to ascertain to what extent the psychological scales differ when they are produced by the several psychophysical methods.
Before proceeding to describe our experiments and the terminology and methods that are involved, it may be in order to de-scribe first the ultimate purposes of the measuring tools that we are here attempting to develop. What might such a tool be used
( 4) for? Perhaps such a question is better answered after a more detailed description of our procedures, but it will be discussed herein order to give as practical a slant as may be possible to the experiments that we have undertaken.
Assume that we want to know which form of appeal is most effective for making people change their minds about a disputed issue such as pacifism, prohibition, municipal ownership, birth control, feminism, on which people differ both as regards the actual convictions which they more or less frankly declare and also as regards the emotional load with which the convictions are adhered to. Would it be more effective to make an appeal to a specified kind of audience by presenting facts in favor of one side of the issue or to present an emotional or oratorical address on the subject? The outcome would supposedly differ with the kind of audience on which the experiment was performed.
If we really want to answer such a question with any particular specifications as to the issue, the two types of appeal to be evaluated, the education, sex, and occupation of the audience, and so on, we should want to evaluate first the distribution of attitudes in our audience before the appeal is made, and then evaluate it after the appeal has been made. A comparison between the distributions of attitudes before and after the presentation of the lecture or reading matter would constitute the natural basis on which we should decide as to which of the two types of appeal would be the more effective in making these people change their minds. But how shall the distribution of attitudes or opinions be measured? That is the main problem of the present investigation.
Another situation that arises frequently enough is that of comparing two groups of people in different localities as to just how strongly they feel on some disputed issue. Of course it is possible merely to present a simple proposition on which the two groups vote "yes"or "no," and the total votes on the single proposition would indicate in a simple but crude way how the two groups feel about the question. But such a total vote does not
( 5) indicate the relative frequency of extreme convictions either for or against the proposition in the two groups, nor does it indicate just how a proposition might be presented in order to command a majority acceptance. If we had a graded series of propositions ranging from one extreme of the issue to the other, then we could present the whole list to the two groups for separate indorsement of each proposition. This is not suggested for popular elections in which the present study has no immediate concern.
On the basis of the resulting tabulations it might be desirable to make a
comparison of the two groups by saying that on the average one of them was more
strongly in favor of the proposition than the other. But what is the average of
the indorsements of a list of propositions? That question could be answered only
if the graded propositions could be assigned to a linear continuum of some sort.
Then it would be possible to locate the central tendency of the frequency
distributions of attitude in the groups, and thereby to compare them by a single
index. In the same manner the two groups could be compared as to the dispersions
of attitude which they represented only in case a measure of dispersion could be
applied to the votes on the list of propositions. A linear continuum is
requisite also for the solution of this problem. Our main problem here concerns
the possibility of measuring attitudes in such a manner.
THE POSSIBILITY OF MEASURING ATTITUDE
The very fact that one offers a solution to a problem so complex as that of measuring differences of attitude on disputed social issues makes it evident from the start that the solution is more or less restricted in nature and that it applies only under certain assumptions that will, however, be described. In devising a method of measuring attitude we have tried to get along with the fewest possible restrictions because sometimes one is tempted to disre-
( 6) -gard so many factors that the original problem disappears. We trust that we shall not be accused of throwing out the baby with its bath.
In promising to measure attitudes we shall make several common-sense assumptions that will be stated here at the outset so that subsequent discussion may not be fogged by confusion regarding them. If the reader is unwilling to grant these assumptions, then we shall have nothing to offer him. If they are granted, we can proceed with some measuring methods that ought to yield interesting results.
It is necessary to state at the very outset just what we shall here mean by the terms "attitude" and "opinion." This is all the more necessary because the natural first impression about these two concepts is that they are not amenable to measurement in any real sense. It will be conceded at the outset that an attitude is a complex affair which cannot be wholly described by any single numerical index. For the problem of measurement this statement is analogous to the observation that an ordinary table is a complex affair which cannot be wholly described by any single numerical index. So is a man such a complexity which cannot be wholly rep-resented by a single index. Nevertheless we do not hesitate to say that we measure the table. The context usually implies what it is about the table that we propose to measure. We say without hesitation that we measure a man when we take some anthropometric measurements of him. The context may well imply with-out explicit declaration what aspect of the man we are measuring, his cephalic index, his height, or weight, or what not. Just in the same sense we shall say here that we are measuring attitudes. We shall state or imply by the context the aspect of people's attitudes that we are measuring. The point is that it is just as legitimate to say that we are measuring attitudes as it is to say that we are measuring tables or men.
The concept "attitude" will be used here to denote the sum-total of a man's inclinations and feelings, prejudice or bias, pre-
( 7) -conceived notions, ideas, fears, threats, and convictions about any specific topic. Thus a man's attitude about pacifism means here all that he feels and thinks about peace and war. It is admittedly a subjective and personal affair.
The concept "opinion" will here mean a verbal expression of attitude. If a man said that we made a mistake in entering the war against Germany, that statement would be called his opinion. The term "opinion" will be restricted to verbal expression. But it is an expression of what? It expresses an attitude, supposedly. There should be no difficulty in understanding this use of the two terms. The verbal expression is the opinion. Our interpretation of such an expressed opinion would be that the man's attitude is pro-German. An opinion symbolizes an attitude.
Our next point concerns what it is that we want to measure. When a man says that we made a mistake in entering the war with Germany, the thing that interests us is not really the string of words as such or even the immediate meaning of the sentence merely as it stands, but rather the attitude of the speaker, the thoughts and feelings of the man about the United States, and the war, and Germany. It is the attitude that really interests us. The opinion has interest only in so far as we interpret it as a symbol of attitude. It is therefore something about attitudes that we want to measure. We shall use opinions as the means for measuring attitudes.
There comes to mind the uncertainty of using an opinion as an index of attitude. The man may be a liar. If he is not intentionally misrepresenting his real attitude on a disputed question, he may nevertheless modify the expression of it for reasons of courtesy, especially in those situations in which frank expression of attitude may not be well received. This has led to the suggestion that a man's action is a safer index of his attitude than what he says. But his actions may also be distortions of his attitude. A politician extends friendship and hospitality in overt action while hiding an attitude that he expresses more truthfully to an intimate
( 8) friend. Neither his opinions nor his overt acts constitute in any sense an infallible guide to the subjective inclinations and preferences that constitute his attitude. Therefore we must remain con-tent to use opinions or other forms of action merely as indices of attitude. It must be recognized that there is a discrepancy, some error of measurement as it were, between the opinion or overt action that we use as an index and the attitude that we infer from such an index.
But this discrepancy between the index and "truth" is universal. When you want to know the temperature of your room, you look at the thermometer and use its reading as an index of temperature just as though there were no error in. the index and just as though there were a single temperature reading which is the "correct" one for the room. If it is desired to ascertain the volume of a glass paperweight, the volume is postulated as an attribute of the piece of glass, even though volume is an abstraction. The volume is measured indirectly by noting the dimensions of the glass or by immersing it in water to see how much water it displaces. These two procedures give two indices which may not agree exactly. In almost every situation involving measurement there is postulated an abstract continuum such as volume or temperature, and the allocation of the thing measured to that continuum is accomplished usually by indirect means through one or more indices. Truth is inferred only from the relative consistency of the several indices, since it is never directly known. We are dealing with the same type of situation in attempting to measure attitude. We must postulate an attitude variable which is like practically all other measurable attributes in the nature of an abstract continuum, and we must find one or more indices which will satisfy us to the extent that they are internally consistent.
In the present study we shall measure the subject's attitude as expressed by the acceptance or rejection of opinions. But we shall not thereby imply that he will necessarily act in accordance with the opinions that he has indorsed. Let this limitation be clear.
( 9) The measurement of attitudes expressed by a man's opinions does not necessarily mean the prediction of what he will do. If his ex-pressed opinions and his actions are inconsistent, that does not concern us now, because we are not setting out to predict overt conduct. We shall assume that it is of interest to know what people say that they believe even if their conduct turns out to be in-consistent with their professed opinions. Even if they are intentionally distorting their attitudes, we are measuring at least the attitude which they are trying to make people believe that they have.
We take for granted that people's attitudes are subject to change. When we have measured a man's attitude on any issue such as pacifism, we shall not declare such a measurement to be in any sense an enduring or constitutional constant. His attitude may change, of course, from one day to the next, and it is our task to measure such changes, whether they be due to unknown causes or to the presence of some known persuasive factor, such as the reading of a discourse on the issue in question. However, such fluctuations may also be attributed in part to error in the measurements themselves. In order to isolate the errors of the measurement instrument from actual fluctuations in attitude, we must calculate the standard error of measurement of the scale itself, and this can be accomplished by methods already well known in mental measurement.
We shall assume that an attitude scale is used only in those situations in which one may reasonably expect people to tell the truth about their convictions or opinions. If a denominational school were to submit to its students a scale of attitudes about the church, one might find that some students hesitate to make known their convictions if they deviate from the orthodox beliefs of their school. At least, the findings could be challenged if the situation in which attitudes were expressed contained pressure or implied threat bearing directly on the attitude to be measured. Similarly, it would be difficult to discover attitudes on sex liberty by a writ-
( 10) -ten questionnaire, because of the well-nigh universal pressure to conceal such attitudes when they deviate from supposed conventions. It is assumed that attitude scales will be used only in those situations that offer a minimum of pressure on the attitude to be measured. Such situations are common enough.
All that we can do with an attitude scale is to measure the attitude actually expressed with the full realization that the subject may be consciously hiding his true attitude or that the social pressure of the situation has made him really believe what he ex-presses. This is a matter for interpretation. It is probably worth while to measure an attitude expressed by opinions. It is another problem to interpret in each case the extent to which the subjects have expressed what they really believe. All that we can do is to minimize as far as possible the conditions that prevent our subjects from telling the truth, or else to adjust our interpretations accordingly.
When we discuss opinions, about prohibition for example, we quickly find that these opinions are multidimensional, that they cannot all be represented in a linear continuum. The various opinions cannot be completely described merely as "more" or "less." They scatter in many dimensions, but the very idea of measurement implies a linear continuum of some sort such as length, price, volume, weight, age. When the idea of measurement is applied to scholastic achievement, for example, it is necessary to force the qualitative variations into a scholastic linear scale of some kind. We judge in a similar way qualities such as mechanical skill, the excellence of handwriting, and the amount of a man's education, as though these traits were strung out along a single scale, although they are, of course, in reality scattered in many dimensions. As a matter of fact, we get along quite well with the concept of a linear scale in describing traits even so qualitative as education, social and economic status, or beauty. A scale or linear continuum is implied when we say that a man has more education than another, or that a woman is more beautiful
( 11) than another, even though, if pressed, we admit that perhaps the pair involved in each of the comparisons have little in common. It is clear that the linear continuum which is implied in a "more and less" judgment may be conceptual, that it does not necessarily have the physical existence of a yardstick.
And so it is also with attitudes. We do not hesitate to compare them by the "more and less'" type of judgment. We say about a man, for example, that he is more in favor of prohibition than some other, and the judgment conveys its meaning very well with the implication of a linear scale along which people or opinions might be allocated.
THE ATTITUDE VARIABLE
The first restriction on the problem of measuring attitudes is to specify an attitude variable and to limit the measurement to that. An example will make this clear. Let us consider the prohibition question and let us take as the attitude variable the degree of restriction that should be imposed on individual liberty in the consumption of alcohol. This degree of restriction can be thought of as a continuum ranging from complete and absolute freedom or license to equally complete and absolute restriction, and it would of course include neutral and indifferent attitudes.
In collecting samples from which to construct a scale we might ask a hundred individuals to write out their opinions about prohibition. Among these we might find one which expresses the belief that prohibition has increased the use of tobacco. Surely this is an opinion concerning prohibition, but it would not be at all serviceable for measuring the particular attitude variable on prohibition mentioned in the foregoing. Hence it would be irrelevant. Another man might express the opinion that prohibition has eliminated an important source of government revenue. This is also an opinion concerning prohibition, but it would not belong to the particular attitude variable that we have set out to measure or scale. It is preferable to use an objective and experimental
( 12) criterion for the elimination of opinions that do not belong on the specified continuum to be measured, and we believe that such a criterion is available.
This restriction on the problem of measuring attitudes is necessary in the very nature of measurement. It is taken for granted in all ordinary measurement, and it must be clear that it applies also to measurement in a field in which the multidimensional characteristics have not yet been so clearly isolated. For example, it would be almost ridiculous to call attention to the fact that a table cannot be measured unless one states or implies what it is about the table that is to be measured; its height, its cost, or beauty, or degree of appropriateness, or the length of time required to make it. The context usually makes this restriction on measurement. When the notion of measurement is applied to so complex a phenomenon as opinions and attitudes, we must here also restrict ourselves to some specified or implied continuum along which the measurement is to take place.
In specifying the attitude variable, the first requirement is that it should be so stated that one can speak of it in terms of "more" and "less," as, for example, when we compare the attitudes of people by saying that one of them is more pacifistic, more in favor of prohibition, more strongly in favor of capital punishment, or more religious than some other person.
Figure i represents an attitude variable, militarism-pacifism, with a neutral zone. A person who usually talks in favor of preparedness, for example, would be represented somewhere to the right of the neutral zone. A person who is more interested in disarmament would be represented somewhere to the left of the neutral zone. It is possible to conceive of a frequency distribution to represent the distribution of attitude in a specified group on the subject of pacifism-militarism.
Consider the ordinate of the frequency distribution at any point on the base line. The point and its immediate vicinity rep-resent for our purpose an attitude, and we want to know relatively
( 13) how common that degree of feeling for or against pacifism may be in the group that is being studied. It is of secondary interest to know that a particular statement of opinion is indorsed by a certain proportion of that group. It is only to the extent that the opinion is representative of an attitude that it is useful for our purposes. Later we shall consider the possibility that a statement of opinion may be scaled as rather pacifistic and yet be indorsed by a person of very pronounced militaristic sympathies. To the extent that the statement is indorsed or rejected by factors other than the attitude variable that it represents, to that extent the
statement is useless for our purposes. We shall also consider an objective criterion for spotting such statements so that they may be eliminated from the scale. In our entire study we shall be dealing, then, with opinions, not primarily because of their cognitive content but rather because they serve as the carriers or symbols of the attitudes of the people who express or indorse these opinions.
There is some ambiguity in using the term attitude in the plural. An attitude is represented as a point on the attitude continuum. Consequently there is an infinite number of attitudes that might be represented along the attitude scale. In practice, however, we do not differentiate so finely. In fact, an attitude, practically speaking, is represented by a certain narrow range or
( 14) vicinity on the scale. When a frequency distribution is drawn for any continuous variable, such as stature, we classify the variable for descriptive purposes into steps, or class-intervals. The attitude variable can also be divided into class-intervals and the frequency counted in each class-interval. When we speak of "an" attitude, we shall refer to a point, or restricted range, on the attitude continuum. Several attitudes will be considered not as a set of discrete entities but as a series of class-intervals along the attitude scale.
A FREQUENCY DISTRIBUTION OF ATTITUDES
The main argument so far has been to show that since in ordinary conversation we readily and understandably describe individuals as more and less pacifistic or more and less militaristic in attitude, we may frankly represent this linearity in the form of a unidimensional scale. This has been done in a diagrammatic way in Figure 1 We shall first describe our objective and then show how a rational unit of measurement may be adopted for the whole scale.
Let the base line of Figure 1 represent a continuous range of attitudes from extreme pacifism on the left to extreme militarism on the right. If the various steps in such a scale were defined, it is clear that a person's attitude on militarism-pacifism could be represented by a point on that scale. The strength and direction of a particular individual's sympathies might' be indicated by the point a, thus showing that he is rather militaristic in his opinions. Another individual might be represented at the point b to show that although he is slightly militaristic in his opinions, he is not so extreme about it as the person who is placed at the point a. A third person might be placed at the point c to show that he is quite militaristic and that the difference between a and c is very slight.A similar interpretation might be extended to any point on the continuous scale from extreme militarism to extreme pacifism, with a neutral or indifference zone between them.
A second characteristic might also be indicated graphically in terms of the scale, namely, the range of opinions that any particular individual is willing to indorse. It is of course not to be expected that every person will find only one single opinion on the whole scale that he is willing to indorse and that he will reject all the others. As a matter of fact we should probably find ourselves willing to indorse several opinions within a certain range of the scale. It is conceivable, then, that a pacifistically inclined person would be willing to indorse all or most of the opinions in the range d to e and that he would reject as too extremely pacifistic most of the opinions to the left of d, and would also reject the whole range of militaristic opinions. His attitude would then be indicated by! the average or mean of the range that he indorses, unless he cares to select a particular opinion which most nearly represents his ownattitude. The same sort of reasoning may of course be extended to the whole range of the scale, so that we should have at least two, or possibly three, characteristics of each person designated in terms of the scale. These characteristics would be (I) the mean position that he occupies on the scale; (2) the range of opinions that he is willing to accept, and (3) that one opinion which he selects as the one which most nearly represents his own attitude on the issue at stake.
It should also be possible to describe a group of individuals by means of the scale. This type of description has been represented in a diagrammatic way by the frequency outline.
Any ordinate of the curve represents the number of individuals, or the percentage of the whole group, that indorses the corresponding opinion. For example, the ordinate at b represents the number of persons in the group who indorse the degree of militarism indicated by the point b on the scale. A glance at the frequency curve shows that for the fictitious group of this diagram militaristic opinions are indorsed more frequently than the pacifistic ones. It is clear that the area of this frequency diagram rep-resents the total number of indorsements given by the group. The
( 16) diagram can be arranged in several different ways that will be separately discussed. It is sufficient at this moment to realize that, given a valid scale of opinions, it would be possible to compare several different groups in their attitudes on a disputed question.
A second type of group comparison might be made by the range or spread that the frequency surfaces reveal. If one of the groups is represented by a frequency diagram of considerable range or scatter, then that group would be more heterogeneous on the issue at stake than some other group whose frequency diagram of attitudes shows a smaller range or scatter. It goes without saying that the frequent assumption of a normal distribution in educational scale construction has absolutely no application here, be-cause there is no reason whatever to assume that any group of people will be normally distributed in their opinions about any-thing.
It should be possible, then, to make four types of description by means of a scale of attitudes. These are (I) the average or mean attitude of a particular individual on the issue at stake; (2) the range of opinion that he is willing to accept or tolerate; (3) the relative popularity of each attitude of the scale for a designated group as shown by the frequency distribution for that group, and (4) the degree of homogeneity or heterogeneity in the attitudes of a designated group on the issue, as shown by the spread or dispersion of its frequency distribution.
This constitutes our objective. The heart of the problem is in the unit of measurement for the base line, and it is to this aspect of the problem that we may now turn.
A UNIT OF MEASUREMENT FOR ATTITUDES
The only way in which we can identify the different attitudes (points on the base line) is to use a set of opinions as landmarks, as it were, for the different parts or steps of the scale. The final scale will then consist of a series of statements of opinion, each of which
( 17) is allocated to a particular point on the base line. If we start with enough statements, we may be able to select a list of forty or fifty opinions so chosen that they represent an evenly graduated series of attitudes. The separation between successive statements of opinion would then be uniform, but the scale can be constructed with a series of opinions allocated on the base line even though their base line separations are not uniform. For the purpose of drawing frequency distributions it will be convenient, however, to have the statements so chosen that the steps between them are uniform throughout the whole range of the scale.
Consider the three statements, a, c, and d, in Figure r. The statements c and a are placed close together to indicate that they are very similar, while statements c and d are spaced far apart to indicate that they are very different. We should expect two individuals scaled at c and a, respectively, to agree very well in discussing pacifism and militarism. On the other hand, we should expect to be able to tell the difference quite readily between the opinions of a person at d and another person at c. The scale separations of the opinions must agree with our impressions of them.
In order to ascertain how far apart the statements should be on the final scale, one method, the method used in our experiment, is to submit them to a group of several hundred people who are asked to arrange the statements in order from the most pacifistic to the most militaristic. We do not ask them for their own opinions. That is another matter entirely. We are now concerned with the construction of a scale with a valid unit of measurement. There may be a hundred statements in the original list, and the several hundred persons are asked merely to arrange the statements in rank order according to the designated attitude variable. It is then possible to ascertain the proportion of the readers who consider statement a to be more militaristic than statement c. If the two statements represent very similar attitudes we should not expect to find perfect agreement in the rank order of statements a and c. If they are identical in attitude, there will be about 50
( 18) per cent of the readers who say that statement a is more militaristic than statement c, while the remaining 50 per cent of the readers will say that statement c is more militaristic than statement a. It is possible to use the proportion of readers or judges who agree about the rank order of any two statements as a basis for actual measurement.
If 90 per cent of the judges or readers say that statement a is more militaristic than statement b (pa> b = 0.90) and if only 60 per cent of the readers say that statement a is more militaristic than statement c (pa> c = 0.60) then clearly the scale separation (a—c) is shorter than the scale separation (a —b). The psychological scale separation between any two stimuli can be measured in terms of a law of comparative judgment.
The practical outcome of this procedure is a series of statements of opinion allocated along the base line of Figure 1. The interpretation of the base-line distances is that the apparent difference between any two opinions will be equal to the apparent difference between any other two opinions which are spaced equally far apart on the scale. In other words, the shift in opinion rep-resented by a unit distance on the base line seems to most people the same as the shift in opinion represented by a unit distance at any other part of the scale. Two individuals who are separated by any given distance on the scale seem to differ in their attitudes as much as any other two individuals with the same scale separation. In this sense we have a truly rational base line, and the frequency diagrams erected on such a base line are capable of legitimate interpretation as frequency surfaces.
In contrast with such a rational base line or scale is the simpler procedure of merely listing from ten to twenty opinions, arranging them in rank order by a few readers, and then merely counting the number of indorsements for each statement. That can of course be done provided that the resulting diagram is not interpreted as a frequency distribution of attitude. If so interpreted the diagram can be made to take any shape we please by merely adding new statements or eliminating some of them, arranging the resulting list in rank order evenly spaced on the base line. Allport's diagrams of opinions are not frequency distributions. They should be considered as bar-diagrams in which is shown the frequency with which each of a number of statements is indorsed. Allport's pioneering studies in this field should be read by every investigator of this problem. Our own interest in the possibility of measuring attitude by means of opinions was started by Allport's article, and the present study is primarily a refinement of his statistical methods.
The ideal unit of measurement for the scale of attitudes is the standard deviation of the dispersion projected on the psycho-physical scale of attitudes by a statement of opinion, chosen as a standard. It is a matter of indifference which statement is chosen as a standard, since the scales produced by using different statements as standards will have proportional scale-values. This mental unit of measurement is roughly comparable to, but not identical with, the so-called "just noticeable difference" in psychophysical measurement. In the present experimental study another unit of measurement was used which will be subsequently de-scribed.
The reason why this ideal unit of measurement, the discrim-
(20) inal error, could not be used in-the present study is as follows: The law of comparative judgment can be used in two ways, neither of which was directly applicable to the present problem for practical rather than for logical reasons. One of these methods is to submit all of the stimuli, in pairs, to the subjects for judgment. Each one of the stimuli is submitted to every subject in combination with every other stimulus in the whole series. For example, two statements would be given to the subject with the request that he indicate which of them is more in favor of the church. When all of the subjects have made their judgments about this pair of statements we can ascertain the proportion, pa>b, of the subjects who think that statement a is more strongly in favor of the church than statement b.
This can of course be done but the task becomes prohibitive, practically, in two ways. In the first place the subjects would be fatigued or bored if they had to make this type of judgment for
pairs of statements, each pair requiring careful reading.
In the second place the statistical labor required to determine the scale-values would also be prohibitive although it is more conceivable than to ask several hundred individuals to read 8,385 pairs of statements.
When the stimuli are more easily and quickly judged than the comparison of two statements, the law of comparative judgment can be readily applied. For example, when the stimuli consist of pairs of nationalities in which the subject is asked only to under-line the nationality that he would in general prefer to associate with, or when the stimuli consist of handwriting specimens presented in pairs so that the subject need only check that specimen which seems the more excellent, then the procedure is not so fatiguing.
The usual psychophysical problem does not involve so many
( 21) stimuli in each series and the number of judgments is thereby reduced to a more reasonable magnitude. The statistical labor is also reduced to proportions more easily handled when the stimulus series is not so long.
Another procedure for the law of comparative judgment is to ask the subject to sort all of the specimens in a series in rank order. When the psychophysical series is much shorter, from fifteen to twenty or even forty, then the task of arranging the stimuli in rank order is not so forbidding. But when the stimulus series consists of 130 statements, most of which must be read every time the subject looks at them for sorting into a rank order, the task becomes unwieldy. Furthermore, the statistical procedures required to extract the proportions, pa>b, for every possible pair of stimuli from absolute rank order data is very laborious.
For these practical reasons it was advisable to use another psychophysical
method in the construction of our attitude scale. We decided to use the method
of equal-appearing intervals which has long been in use in psychophysical
experimentation. The detailed experimental application of this method to the
construction of our attitude scale will now be described.