Pdsq scoring

Psychiatric Diagnostic Screening Questionnaire

Review of The Psychiatric Diagnostic Screening Questionnaire by MICHAEL G. KAVAN, Associate Dean for Student Affairs and Associate Professor of Family Medicine, Creighton University School of Medicine, Omaha, NE:

DESCRIPTION. The Psychiatric Diagnostic Screening Questionnaire (PDSQ) is a self-report instrument designed to screen for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV; American Psychiatric Association, 1994) Axis I disorders that are most commonly seen in medical and outpatient mental health settings. It is designed to be completed by individuals 18 years of age and older prior to their initial diagnostic interview. The PDSQ covers 13 Axis I areas including Major Depressive Disorder, Posttraumatic Stress Disorder, Bulimia/Binge-Eating Disorder, Obsessive-Compulsive Disorder, Panic Disorder, Psychosis, Agoraphobia, Social Phobia, Alcohol Abuse/Dependence, Drug Abuse/Dependence, Generalized Anxiety Disorder, Somatization Disorder, and Hypochondriasis. It also provides a PDSQ Total score, which acts as a global measure of psychopathology.

According to the manual, the PDSQ is designed to be used in "any clinical or research setting where screening for psychiatric disorders is of interest" (manual, p. 2). It may be administered and scored by any appropriately trained and supervised technician; however, clinical interpretation should only be undertaken by a professional with appropriate psychometric and clinical training.

The PDSQ consists of 125 items in which respondents are requested to answer yes or no to each test booklet question according to "how you have been acting, feeling, or thinking" during the past 2 weeks or 6 months, depending on the symptom cluster. Typical administration time is between 15 and 20 minutes. Scoring is completed by hand and entails counting the number of yes responses on each PDSQ subscale and entering that number in the space provided on the accompanying summary sheet. Subscale scores are then compared to cutoff scores to determine whether follow-up interviewing is indicated. In addition, the scorer is to circle critical items to which the respondent answered "yes." All subscale scores are then summed in order to obtain a PDSQ Total raw score. Finally, the PDSQ Total raw score is transferred to a PDSQ Score Conversion table that converts the total score into a T-score. On the back side of the summary sheet is a table that includes diagnosis percentages of persons who endorsed each item and either qualified or failed to qualify for a subscale diagnosis. An accompanying CD provides follow-up interview guides for all 13 disorders. These may be printed and then used to gather additional diagnostic information regarding these syndromes.

As noted previously, scores from the PDSQ are then used to facilitate the initial diagnostic evaluation. The author notes that "results should be verified whenever possible against all available information, including the results of patient interviews, clinical history, professional consultations, service agency records, and the results of additional psychological tests" (manual, p. 11).

DEVELOPMENT. The PDSQ was developed to be a relatively brief, self-administered questionnaire for the assessment of various DSM-IV Axis I disorders in psychiatric patients. Development of the measure began over 10 years ago with an instrument entitled the SCREENER, which was originally designed to screen for psychiatric disorders in primary care settings and later in outpatient mental health settings. Following subscale revisions, the SCREENER became a 102-item version of the PDSQ. Through additional modifications the PDSQ took its present form as a scale of 125 items.

TECHNICAL. The author stresses the importance of patients being able to understand any self-administered instrument. As such, readability studies of the initial version of the PDSQ were conducted and ranged from a 5.8 grade level (Flesch-Kincaid method) to a 9.2 grade level (Bermuth formula). Additional understandability studies using psychiatric outpatients demonstrated that PDSQ items were "written at a level that most individuals ... would understand" (manual, p. 27). The author acknowledges that one-third of the sample patients were college graduates and only 5% of the sample patients had less than a high school diploma.

Initial and replication studies were conducted to estimate internal consistency and test-retest reliability on 112- and 139-item versions of the PDSQ. Samples were large, but dominated by white, married or single, and educated females. Internal consistency values (Cronbach alpha) for the initial study on 732 psychiatric outpatients ranged from .73 (Somatization Disorder) to .95 (Drug Abuse/Dependence), whereas a replication study involving 994 psychiatric outpatients found internal consistency estimates to range from .66 (Psychosis and Somatization Disorder) to .94 (Posttraumatic Stress Disorder). Test-retest reliability coefficients on a subsample of these patients ranged from .66 (Bulimia/Binge-Eating Disorder) to .98 (Drug Abuse/Dependence) for the initial study (mean interval of 4.8 days) and from .61 (Mania/Hypomania) to .93 (Drug Abuse/Dependence) in the replication study (mean interval of 1.6 days).

The author reports that 27 of the 112 items did not achieve a minimum endorsement base rate of 5% during the initial study and were not used to determine test-retest reliability. Eighty-three of the 85 remaining items had a Cohen's kappa coefficient, which corrects for chance levels of agreement, between .67 and .92. In the replication study, only two items were excluded in the test-retest reliability study. Cohen's kappa for the remaining items ranged from .50 to .83. Although there is some disagreement regarding the interpretation of kappa, Spitzer, Fleiss, and Endicott (1978) suggest that values greater than .75 demonstrate good reliability, values between .50 and .75 suggest fair reliability, and values below .50 connote poor reliability. In the initial study, 7 subscales (Major Depressive Disorder, Dysthymic Disorder, Bulimia/Binge-Eating Disorder, Mania/Hypomania, Agoraphobia, Generalized Anxiety Disorder, and Hypochondriasis) would be considered to have fair reliability and 7 (PTSD, Obsessive-Compulsive Disorder, Panic Disorder, Psychosis, Social Phobia, Alcohol Abuse/Dependence, and Somatization Disorder) would be considered to have good reliability (1 subscale did not meet the base rate standard). In the replication study, 14 subscales would be considered to have fair reliability and 1 (Drug Abuse/Dependence) would be considered to have good reliability.

To document discriminant and convergent validity, corrected item/subscale total correlation coefficients were calculated between each item and subscale. The mean of the correlations between each subscale item and that subscale's total score were compared to the mean of correlations between each subscale item and the other 14 subscale scores. The author points out that in 90.2% of the calculations the item/parent-subscale correlation was higher than each of the item/other-subscale correlations. A similar pattern emerged from the replication study with 97.1% of items having a higher correlation with their parent subscale. Data are not provided on correlations between each subscale mean and other individual subscales within the PDSQ.

The PDSQ subscales were also compared to "other measures of the same construct versus measures of different constructs" (manual, pp. 31-32). In all instances, the PDSQ subscale scores were significantly correlated with measures of similar syndromes. In addition, correlations were higher between scales assessing the same symptom domain than scales assessing other symptom domains. Interpretation is somewhat clouded by the manual's lack of clarity regarding the nature of these measures.

Finally, criterion validity was documented by comparing the scores of respondents with and without a particular DSM-IV diagnosis. In both the initial and replication studies, the average PDSQ score was significantly higher for those with versus those without the disorder (the only exception was Mania-Hypomania, which was subsequently dropped from the PDSQ).

Cutoff scores are provided based on a study of 630 psychiatric outpatients who were interviewed with the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID; First, Spitzer, Gibbon, & Williams, 1997). Based on results from this study and the fact that the PDSQ is intended to be used as an aid for conducting an initial diagnostic evaluation, the author has recommended a cutoff score resulting in diagnostic sensitivity of 90%. These cutoff scores are provided on the PDSQ Summary Sheet. In addition, a table within the manual includes cutoff scores, sensitivity, negative and positive predictive values, and separate columns estimating the rates of occurrence among psychiatric patients and the general population-the latter being based on information obtained from the DSM-IV.

Limited data are provided within the manual on the PDSQ Total Score. The author states that it is the only norm-referenced score in the instrument. The Total Score is expressed as a standard T-score and is a means for "comparing the patient's level of symptom endorsement with that of the average patient seen for intake in a clinical psychiatric outpatient setting" (manual, p. 11). Apparently, it provides a "rough measure of the overall level of psychopathology and consequent dysfunction that a patient reports" (manual, p. 11). However, the author states that it is only loosely related to the distress a patient may be experiencing and it should not be used as an index of severity.

COMMENTARY. The purpose of the PDSQ is to screen for DSM-IV Axis I disorders that are most commonly seen in outpatient mental health settings. With any measure such as this, the real question is: Is it accurate and does it improve efficiency? In regard to accuracy, the PDSQ has respectable internal consistency and test-retest reliability. In addition, convergent and discriminate validity studies demonstrate that PDSQ items are correlated more strongly with their parent subscale than with other subscales within the PDSQ. Also, the PDSQ items were more strongly correlated with other measures of the same construct versus measures of different constructs; although the manual is somewhat unclear as to the nature of these "measures." Finally, it appears as though the PDSQ has decent sensitivity and specificity and does well at identifying both principal and comorbid disorders. A problem, however, is that the PDSQ has no validity indices, thereby allowing patients to misrepresent themselves on the instrument. Any interpretation should, therefore, be done cautiously and with corroborating information.