Journal of the National Cancer Institute Advance Access originally published online on February 26, 2008
JNCI Journal of the National Cancer Institute 2008 100(5):333-346; doi:10.1093/jnci/djn027
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© The Author 2008. Published by Oxford University Press.
ARTICLES |
Promoting Regular Mammography Screening I. A Systematic Assessment of Validity in a Randomized Trial
Affiliations of authors: Center for Clinical and Translational Sciences, University of Texas Health Science Center at Houston, Houston, TX (DJdJ); Division of Health Promotion and Behavioral Sciences, University of Texas-Houston School of Public Health, Houston, TX (SWV, SPC, DRL, WC, AM); Cancer Prevention Fellowship Program, Office of Preventive Oncology, Division of Cancer Control and Population Sciences, National Cancer Institute, Bethesda, MD (JAT); Center for Health Services Research in Primary Care, Durham VA/Duke University, Durham, NC (LAB); Section of General Medicine, Department of Medicine, Baylor College of Medicine, Houston, TX (LSS); Department of Psychology, University of Houston-Victoria, Victoria, TX (CAP); School of Math, Science and Technology, Elizabeth City State University, Elizabeth City, NC (CW); Department of Community Health, Brown University, Providence, RI (WR)
Correspondence to: Deborah J. del Junco, PhD, Center for Clinical and Translational Sciences, University of Texas Health Science Center at Houston, 6410 Fannin St, LL.125, Houston, TX 77030 (e-mail: deborah.j.deljunco{at}uth.tmc.edu).
Background: Most health promotion trials in cancer screening offer limited evidence of external validity. We assessed internal and external validity in a nationwide, population-based trial of an intervention to promote regular mammography screening.
Methods: Beginning in September 2000, study candidates age 52 years and older (n = 23000) were randomly selected from the National Registry of Women Veterans and sent an eligibility survey. Consistent with intention-to-treat principles for effectiveness trials, we randomly assigned eligible respondents and nonrespondents to one of five groups. We mailed baseline surveys to groups 1–3 followed by intervention materials of varying personalization to groups 1 and 2. We delayed mailing baseline surveys to two additional control groups to coincide with the mailing of postintervention follow-up surveys to groups 1–3 at year 1 (group 4) and year 2 (group 5). Mammography rates were determined from self-report and Veterans Health Administration records. To assess internal validity, we compared groups on participation and factors associated with mammography screening at each stage. To assess external validity, we compared groups 3, 4, and 5 on mammography rates at the most recent follow-up to detect any cueing effects of prior surveys and at the respective baselines to uncover any secular trends. We also compared nonparticipants with participants on factors associated with mammography screening at the trial's end.
Results: We established study eligibility for 21340 (92.8%) of the study candidates. Groups 1–3 were similar throughout the trial in participation and correlates of mammography screening. No statistically significant survey cueing effects or differences between nonparticipants and participants across groups were observed. Mammography screening rates over the 30 months preceding the respective baselines were lower in group 5 (82.3% by self-report) than in groups 1–4 (85.1%, P = .024, group 5 vs groups 1–4 combined), suggesting a decline over time similar to that reported for US women in general.
Conclusion: This systematic assessment provides evidence of the trial's internal and external validity and illustrates an approach to evaluating validity that is readily adaptable to future trials of behavioral interventions.
| CONTEXT AND CAVEATS Prior knowledge Trials to assess interventions to change behavior often evaluate internal validity or the efficacy of the intervention under optimal conditions. However, they are rarely set up to evaluate external validity, that is, the intervention's likely effectiveness in the broad population. Study design A nationwide, population-based trial of US women veterans to evaluate an intervention to promote regular mammography, Project Healthy Outlook on the Mammography Experience, was designed to address both internal and external validity. Internal validity was assessed by comparing intervention groups on participation and factors associated with mammography screening; external validity was assessed by establishing additional control groups to evaluate survey "cueing" effects and general population trends and by comparing characteristics of nonparticipants with those of participants. Contributions The intervention groups were similar, indicating that the trial is likely to be internally valid. There was no evidence that completing the baseline or interim follow-up surveys by themselves led to an increase in mammography. The external validity assessment revealed a decline in mammography over time similar to that seen in the broader US population. Finally, there were no statistically significant between-group differences comparing nonparticipants with participants. Implications The trial is likely to be both internally and externally valid. The approach used by the authors is adaptable to studies of other behavior change interventions. Limitations Many women veterans obtain health care outside the Veterans Administration system, so complete ascertainment of mammography in nonparticipants was not possible. This type of under-ascertainment would be expected to reduce only slightly the magnitude of the study's intention-to-treat estimates of intervention effectiveness.
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Manuscript received August 7, 2007; revised December 7, 2007; accepted January 16, 2008.
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  S. W. Vernon, D. J. del Junco, J. A. Tiro, S. P. Coan, C. A. Perz, L. A. Bastian, W. Rakowski, W. Chan, D. R. Lairson, A. McQueen, et al. Promoting Regular Mammography Screening II. Results From a Randomized Controlled Trial in US Women Veterans J Natl Cancer Inst, March 5, 2008; 100(5): 347 - 358. [Abstract] [Full Text] [PDF]
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