The PQ is a 92-item self-report questionnaire that takes approximately 20 minutes to complete. Items are answered True/False and sum to form four major scales: 1) positive symptoms (unusual thinking, perceptual abnormalities and cognitive disorganization); 45 items, 2) negative symptoms (e.g. flat affect, social isolation); 19 items, 3) disorganized symptoms (e.g. odd behavior); 13 items, and 4) general/affective symptoms (e.g. depression, role functioning); 14 items. Item domains are parallel to scales from the SIPS and include items from the Schizotypal Personality Questionnaire (SPQ; Raine 1991) as well as the SIPS, plus additional items. Sample items include “Sometimes I think that people can read my mind,” and “I tend to avoid social activities with other people.” Participants are asked to rate their experiences in the last month and are instructed NOT to include any experiences that occurred while using alcohol or street drugs.
Several modifications were made to adapt the PQ for use with a non-clinical sample and to address the specific hypotheses of this project. In the CAPE study (Hanssen et al., 2003
), an association was found between help-seeking or distress about attenuated psychotic symptoms and risk for psychosis. In order to assess rates of help-seeking and distress, the PQ was first modified (PQ-T/F) for the present study by asking subjects if they had sought or received any psychiatric or psychological treatment in the past month, and when an item was endorsed, the subjects were asked if they were distressed by that experience. We were also interested in the frequency of experiences in the general population, given the SIPS criterion for prodromal syndromes that attenuated level symptoms occur at least weekly. We hypothesized that although many students might endorse psychotic-like experiences (PLEs), few students experience them frequently. In a second revision (PQ-Likert), we replaced the true/false response format with Likert-scale response options assessing the frequency of experiences (“never,” “one to two times per month,” “once per week,” “few times per week,” or “daily”). Additionally, six items were rephrased and reverse-coded to check reliability of responding.
2.2 Participants and assessments
Undergraduate students (N=1,020) aged 18 years and older who were enrolled in Introductory Psychology courses at UCLA completed the PQ anonymously as part of a packet of questionnaires at the beginning of class during the first week of the course. Participants gave informed consent and were given the option to refuse any or all questions on the surveys. Refusals per class were not documented, but response rate per quarter, when compared to class sizes, suggests that the refusal rate was negligible. The study protocol and informed consent procedures were approved in advance by the UCLA IRB. Students who participated during the first academic quarter in which this study was conducted completed the PQ-T/F (N=271). The decision to assess frequency of experiences led to subsequent changes, students who participated during the following three academic quarters completed the PQ-Likert (N=749). presents demographic information for the samples.
2.3 Validity check
In order to assess random or inaccurate responding, students were asked to indicate whether they had read the instructions at the beginning of the questionnaire. Comparisons of PQ scale scores of instruction-readers versus non-readers were conducted using Wilcoxon rank sum tests, which suggested that both groups were likely sampled from the same population. Therefore, both groups of participants were used in the present analyses. On the PQ-Likert, six items were rephrased in the opposite direction and reverse-coded, with both items presented in the measure (e.g. “I have not been sleeping well lately” and “I have been sleeping well lately.”) Difference scores on the six item pairs were summed to form a reliability score, where higher scores are more unreliable. Twenty students with poor reliability scores (> 3 SD above the mean) were consequently deleted from all analyses in this paper, leaving 749 subjects in the PQ-Likert group.
2.4 Statistical Analyses
Given the positively skewed distribution of PQ scores, non-parametric tests were used for all comparisons. The very small proportion of help-seekers in this study created grossly unequal sample sizes when comparing the PQ scores of those who reported seeking mental health treatment to those who did not. Therefore, Fisher’s exact test was used with 2X2 contingency tables that calculated the proportion of help-seekers and non-help-seekers in each half of the PQ scale score distributions, split at the median value for that scale. Additionally, separate logistic regressions were performed with each PQ scale as the independent variable and help-seeking as the dependent variable, along with stepwise logistic regressions that entered all PQ scales as independent variables, for both samples. Unfortunately, the low base rates of help-seeking (PQ-T/F, N=12; PQ-Likert, N=23) and items endorsed as distressing created undue influence of individual scores within the help-seeking group. As a result, we were unable to compare distressing items between help-seekers and other students. All statistical analyses were completed using SAS 8.2.