The Minnesota Multiphasic Personality Inventory

(MMPI) is a questionnaire used to gauge personality type. Several scales are built into the MMPI to assess response distortion; these include the Infrequency (I), Obvious (0), Subtle (S), Obvious-subtle (0-S), and Dissimulation (D) scales. Psychological Assessnlent

(Mar. 1995) published a study that investigated the effcctiveness of these MMPI scales in detecting deliberately distorted responses. An independent sampling design with four treatments was employed. The treatments consisted of independent random samples of females in the following four groups: nonforensic psychiatric patients (n, = 65), forensic psychiatric patients (n, = 28), college students who were requested to respond honestly (n, = 140), and college students who were instructed to provide "fake bad"

responses (n, = 45). All 278 participants were given the MMPI and the I, 0, S, 0-S, and D scores were recorded for each. Each scale was treated as a response variable and an analysis of variance conducted. The ANOVA F values are reported in the table.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Response Variable ANOVA F Value Infrequency (I) 155.8 Obvious (0) 49.7 Subtle (S) 10.3 Obvious-subtle (0-S) 45.4 Dissimulation (D) 39.1

a. For each response variable, determine whether the mean scores of the four groups completing the MMPI differ significantly. Use a = .05 for each test.

b. If the MMPI is effective in detecting distorted responses, then the mean score for the "fake bad treatment group will be largest. Based on the ~nformation provided, can the researchers make an inference about the effectiveness of the MMPI?

Explain.