No Significant Differences Are Found Between Three Groups In. Their Susceptibility To The Barnum Effect. Christina K. Edmondson

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1 Susceptibility to the Barnum Effect 1 Running head: SUSCEPTIBILITY TO THE BARNUM EFFECT No Significant Differences Are Found Between Three Groups In Their Susceptibility To The Barnum Effect Christina K. Edmondson San Jose State University

2 Susceptibility to the Barnum Effect 2 Abstract This experiment investigated the Barnum effect, individuals tendency to see vague personality descriptions as true and unique. Participants were college psychology students and their recruits 21 males and 74 females (11- to 52-year-old). An online survey program instructed 95 participants to complete a demographic information survey, and randomly divided them into 3 groups: 25, control (rated a generalized personality profile only); 45, placebo (provided geometric shape preferences before rating); and 25, treatment (provided birth information before rating) groups. Previous studies had reported higher ratings when individuals believe the profile is birth information based rather than generalized. This experiment found no significant differences between the 3 groups ratings (a=0.05). Further studies that randomly select participants and equalize group size are suggested.

3 Susceptibility to the Barnum Effect 3 The Study Found No Significant Differences Between Three Groups In Their Susceptibility To The Barnum Effect The Barnum effect refers to the tendency of people to often see vague and general statements contained in personality tests as both true and applicable only to themselves (Piper- Terry & Downey, 1998). In one experiment studying the Barnum effect phenomenon, Snyder and Larsen asked the participants to rate the accuracy of a generalized personality profile that was supposedly based on one of the three assessment procedures: psychological, graphological and astrological. A control group, which was told that the personality profile given was generalized, also rated the accuracy of the personality profile along with the other groups. Snyder and Larsen found no significant differences in the rating of a generalized personality profile that was supposedly based on psychological, graphological, or astrological assessment procedures. However, participants in the control condition rated the accuracy of a generalized personality profile lower than the participants in other three conditions (Snyder & Larsen, 1976). Glick, Gottesman, and Jolton supported the finding of Snyder and Larsen in an experiment examining the susceptibility of astrology skeptics and believers to the Barnum effect. They found that both skeptics and believers rated the supposedly personalized personality descriptions based on their birth information (birth date, time and location) as more accurate than the generalized personality descriptions (the same descriptions as the supposedly personalized personality descriptions). This phenomenon applied to both positive and negative personality descriptions (Glick et al., 1989). This experiment followed from the studies conducted by Snyder and Larsen, and Glick et al. In contrast to those studies, a placebo group, which was surveyed on their geometric shape preference before rating generalized personality profile, was included in this experiment in

4 Susceptibility to the Barnum Effect 4 addition to the control (rating task only) and treatment groups (birth information survey and rating task). The purpose of this experiment was to test the hypothesis that participants in the treatment group would rate their personality profile higher than participants in the placebo group or the control group. Method Participants There were 95 participants in the experiment. The participants consisted of college students taking psychology classes during the Spring 2001 semester and volunteers who were recruited by these students. The college students participated in this experiment as a part of the psychology class assignments. The mean age of the participants was 24.25, with individual participants ranging from 11- to 52-years old (see Tables 1 and 2 for more details). Twenty-one participants in the experiment were male and 74 were female. The participants were randomly assigned to one of the three groups. Apparatus This experiment used an online survey program. There were several surveys contained in the on-line survey program. For this study, only data collected from four surveys were analyzed: a demographic information survey (age and sex), a birth information survey (date, time, and country), a geometric shape preference survey, and a personality profile rating survey (on a 1 to 7 scale). The content of the surveys is shown in Appendices A, B, C, and D. While all participants were instructed to complete the demographic information survey and personality profile rating survey, not all participants were assigned to complete the birth information survey and geometric shape preference survey. Procedure

5 Susceptibility to the Barnum Effect 5 The online survey program first instructed all participants to respond to the demographic information survey. The online survey program then randomly assigned the participants into one of the three groups: 1) control, 2) placebo, and 3) treatment groups. The online survey program instructed the participants in the control group to read a personality profile (generalized) and rate the accuracy between the personality profile and the participant s personality on a 1 to 7 scale (1- not at all accurate; 7-extremely accurate). For participants in the placebo group, the online survey program instructed them to select 1 of 3 geometric shapes in 5 different trials; then to read and rate the same personality profile in the same manner as in the control group. The participants in the treatment group typed in their dates, time, and countries of birth, read and rated the same personality profile in the same manner as the participants in the other two groups. The online survey program recorded the participant responses. Results The online survey program randomly assigned 45 participants to the control group, 25 participants to the placebo group, and 25 participants to the treatment group. The mean of the personality profile ratings for the control group was 4.76 (SD=1.30). The mean for the placebo group was 4.87 (SD=1.74). Finally, the mean for the treatment group was 4.92 (SD=1.58) (see Table 3). The one-way ANOVA of the three groups and their personality profile ratings revealed that the differences of personality profile ratings between these groups were not significant, F(2,92)=.066, p=n.s. (a=0.05) (see Table 4). Discussion Contrary to the findings of Snyder and Larsen, and Glick et al., the results of this experiment failed to support the experimental hypothesis. There were no significant differences in the ratings of personality profiles between individuals providing birth information, individuals

6 Susceptibility to the Barnum Effect 6 giving geometric shape preference, and individuals supplying no information before rating the generalized personality profile. Two of the possible explanations for the failure to support the experimental hypothesis are the participant selection process and assignment process. The participants in this experiment were not randomly selected; instead, a sample of convenience was used. They were psychology students or individuals who were affiliated with these students. Therefore, the participants in this experiment were more likely to be aware of the Barnum effect, and to be skeptical toward personality assessment based on limited information (such as birth information and geometric shape preference). The overrepresentation of female participants in this experiment may also have affected the experimental outcome. Since the online survey program did not ensure that equal numbers of participants were randomly assigned to each group, there were 45 participants in the placebo group versus 25 participants in each of the control and treatment group. The unequal distribution of the participants may also have impacted the findings of this experiment. Future similar experiments should randomly select the participants and randomly assign equal numbers of participants to each group to provide more insight into the Barnum effect phenomenon.

7 Susceptibility to the Barnum Effect 7 Reference Glick, P., Gottesman D., & Jolton J. (1989). The fault is not in the stars: Susceptibility of skeptics and believers in astrology to the Barnum effect. Personality and Social Psychology Bulletin, 15 (4), Piper-Terry, M.L. & Downey, J.L. (1998). Sex, gullibility, and the Barnum effect. Psychological Reports, 82, Snyder C.R. & Larsen, D.L. (1976). Acceptance of general personality interpretations prior to an dafter receipt of diagnostic feedback supposedly based on psychological, graphological, and astrological assessment procedures. Journal of Clinical Psychology, 32 (2),

8 Susceptibility to the Barnum Effect 8 Table 1 Mean age of male and female participants Age Sex N M SD Male Female Total

9 Susceptibility to the Barnum Effect 9 Table 2 Age of the Participants Age N Total 95

10 Susceptibility to the Barnum Effect 10 Table 3 Personality Profile Rating for the Three Groups Group N M SD Control Placebo Treatment Total Note. Individuals in the control group didn t perform any task before rating the personality profile. Individuals in the placebo group provided their geometric shape preferences, while individuals in the treatment group supplied their birth information before rating the personality profile.

11 Susceptibility to the Barnum Effect 11 Table 4 Analysis of Variance for Personality Profile Ratings Source SS df MS F p Between Groups Within Groups Total

12 Susceptibility to the Barnum Effect 12 Appendix A: Demographic Survey Thank you for your participation. To begin please provide the information requested below: Your age Sex Male Female NEXT >

13 Susceptibility to the Barnum Effect 13 Appendix B : Geometric Shape Preferences Survey Select a shape by clicking on it B G R Select a shape by clicking on it B B B Select a shape by clicking on it G G G Select a shape by clicking on it B G R Select a shape by clicking on it R G B Note. The letters R, G, B, reflect the colors of the geometric shapes shown on the survey.

14 Susceptibility to the Barnum Effect 14 Appendix C: Birth Information Survey Please provide the following information: Birth Date ( Ex: 12/24/75) Birth Time Country of Birth (Ex: 10:30 am) ( Ex: Argentina) NEXT >

15 Susceptibility to the Barnum Effect 15 Appendix D: Personal Profile Rating Your Personality Profile: You have a need for other people to like and admire you, and yet you tend to be critical of yourself. While you have some personality weaknesses you are generally able to compensate for them. You have considerable unused capacity that you have not turned to your advantage. Disciplined and self-controlled on the outside, you tend to be worrisome and insecure on the inside. At times you have serious doubts as to whether you have made the right decision or done the right thing. You prefer a certain amount of change and variety and become dissatisfied when hemmed in by restrictions and limitations. You also pride yourself as an independent thinker; and do not accept others' statements without satisfactory proof. But you have found it unwise to be too frank in revealing yourself to others. At times you are extroverted, affable, and sociable, while at other times you are introverted, wary, and reserved. Some of your aspirations tend to be rather unrealistic. How accurate is this description of you? (select one of the choices below) Not at all Accurate Extremely Accurate Submit