The Contamination Survey Health Status Questionnaire (HSQ) is designed to assess the rate of prostate, lung, colorectal and ovarian screening that occurred outside the trial protocol. Data from the HSQ provide an estimate of the contamination rate in the PLCO trial.
The survey contains questions about various types of exams, including the PLCO screening exam types. For each exam, the participant was asked three questions: whether they received the exam, how recently they received the exam, and the reason for the exam. For the exam types used in the PLCO screening protocol, intervention arm participants were explicitly asked to report an exam only if it occurred after their last PLCO screening exam of that type.
Initially, the HSQ asked each participant about eight gender-neutral exams; in addition, men were asked about two gender-specific exams and women were asked about four gender-specific exams. In 2004, the Spiral CT exam was added to the HSQ. In 2005, the blood in stool exam was added. As a result, starting in 2005, men were asked about 12 exams and women were asked about 14 exams.
The survey was administered to a randomly selected sample of participants in the years 1997, 1999 - 2005, 2007, 2009 and 2010. A new random sample was selected for each of the eleven survey years. Samples were stratified by gender, screening center, and study year. Additional selection criteria are addressed below.
The sampling criteria changed over time:
- 1997 - 2003: During this time period, approximately 1,000 participants were selected each year. Only "uncontaminated controls" were eligible for sampling. "Uncontaminated controls" are defined as control arm participants who had not reported undergoing 2+ PSA exams or 1+ colorectal exams (flexible sigmoidoscopy / colonoscopy / barium enema) in the three years prior to trial entry. Information on screening prior to trial entry ("baseline contamination") was obtained from the baseline questionnaire (BQ).
2004 - 2010: During this time period, approximately 2,000 participants were selected each year. Participants were distributed among the following groups:
- ~1000 "uncontaminated controls" defined above.
- ~200 "contaminated controls" defined as control arm participants who reported undergoing 2+ PSA exams or 1+ colorectal exams in the three years prior to trial entry.
- ~800 intervention arm participants who were in study year T7 or later. These participants were beyond the screening period of the trial.
In total, approximately 13,000 participants were surveyed. Some participants happened to be selected in two or three separate years. The HSQ data contain information on only a subset of PLCO participants, some of whom have more than one record in the dataset, and therefore care should be taken when merging with other PLCO data.
HSQ data can be obtained through the HSQ dataset.