Development of the Decision-Aid
We conducted 2 focus groups to develop the content of the decision-aid. The focus group participants were similar to the target population: veterans aged 50 to 80 years who were receiving primary care at the VAMC. The Health Belief Model was used as the theoretical framework from which to probe focus group members regarding their knowledge and beliefs about prostate cancer screening.16,17 We found that patients had a general awareness of the prevalence of prostate cancer but expressed significant knowledge deficits and misinformation about risk factors, symptoms, screening recommendations, risk and benefits, treatment options, and prognosis for prostate cancer. We designed the content of the decision-aid to address the deficits in knowledge most striking in the focus groups.
The decision-aid included quantitative information on the operating characteristics (sensitivity and specificity) of a combined screening strategy of DRE and PSA and a description of follow-up tests (TRUS and prostate biopsy). Interpretation of probability outcomes are subject to many biases, including framing and presentation effects.18-20 We tried to present prostate cancer screening outcomes in a balanced manner. The graphic design used to convey the sensitivity and specificity of a prostate cancer screening strategy consisted of human figure representations Figure 1. An illustration presented 100 male human figures. A subset of figures was highlighted to represent the frequency of abnormal screening test results (10/100), true-positive test results (3/100), false-positive test results (7/100), and false-negative test results (1/100). Although treatment was not the focus of the intervention, treatment efficacy is one element of the total risks and benefits associated with prostate cancer screening. In the framework of the Health Belief Model, perceptions of treatment efficacy may influence screening behavior. We included a statement on the uncertain efficacy of treatment of early-stage prostate cancer in the decision-aid intervention.
The comparison intervention consisted of a written pamphlet containing basic prostate cancer information (epidemiology, symptoms of prostate cancer, prostate cancer screening methods, and the potential benefits of screening) but excluding the quantitative and qualitative outcomes regarding risks and benefits of screening that were included in the decision-aid. The basic prostate cancer information was also included in the decision-aid. Pamphlets were printed in a 14-point font to facilitate reading for older subjects. The comparison and experimental pamphlets were 5 and 8 pages in length, respectively.
Outcome Assessments
We used a prostate cancer knowledge assessment survey to evaluate the following domains: risk factors and incidence of prostate cancer, clinical presentation of prostate cancer, test characteristics of the DRE and the PSA, confirmatory tests (TRUS and prostate biopsy), and the natural history of prostate cancer. A prostate cancer belief-assessment survey was used to evaluate subjects’ perceptions of available screening tests and their intended screening behavior. Domains in the belief assessment included the natural history of prostate cancer, intentions to use prostate cancer screening, intentions to follow the physician’s advice on screening, perceptions of test characteristics, and how well informed they felt about screening options. The knowledge and belief assessment surveys consisted of 18 and 10 closed-ended items, respectively. The items were pilot-tested with 30 subjects who had demographic characteristics similar to those of the study population, and the format of items was revised accordingly. Test-retest reliability of single questions for correct/incorrect responses on the knowledge assessment were between 0.56 and 1.00 (average=0.82).
Prostate cancer screening use was ascertained from the follow-up physician visit. Subjects were asked if they wanted to be screened for prostate cancer with DRE or PSA, or both DRE and PSA. If they responded affirmatively, they were given the screening test at that study visit. A subject was considered to have chosen prostate cancer screening if he answered yes to having both the DRE and the PSA and proceeded to have those tests. For patients who had no rectum because of previous gastrointestinal surgery (n=3), a completed PSA met criteria for having chosen prostate cancer screening.
Statistical Methods
The knowledge survey was analyzed as total correct score and individual questions. Total knowledge scores on postintervention assessments were compared between groups using a Wilcoxon-Mann-Whitney test. When comparing the preintervention and postintervention responses to individual knowledge questions, subjects were assigned to 1 of 4 categories: (a) change in response from incorrect to correct, (b) incorrect response on both the pretest and the posttest, (c) correct response on both pretest and posttest, or (d) change in response from correct to incorrect. We used a chi-square analysis to compare categories of pre-post response pairs between the experimental and comparison groups. Postintervention responses to belief assessment items and use of prostate cancer screening (as defined by having both a DRE and a PSA test) were compared between groups with a chi-square analysis. Our study had a power of 0.80 to determine a 15% difference in the proportion of patients deciding to have prostate cancer screening, assuming that the baseline level of screening in the population was 80% and using a 2-sided test with an a of 0.05.