The validity of self-reported cancer screening history and the role of social disadvantage in Ontario, Canada
Aisha Lofters
0
1
Mandana Vahabi
0
Richard H Glazier
0
1
0
Centre for Research on Inner City Health, Li Ka Shing Knowledge Institute, St. Michael's Hospital
,
Toronto
,
Canada
1
St. Michael's Hospital Department of Family and Community Medicine, University of Toronto
,
Toronto
,
Canada
Background: Self-report may not be an accurate method of determining cervical, breast and colorectal cancer screening rates due to recall, acquiescence and social desirability biases, particularly for certain sociodemographic groups. Therefore, the aims of this study were to determine the validity of self-report of cancer screening in Ontario, Canada, both for people in the general population and for socially disadvantaged groups based on immigrant status, ethnicity, education, income, language ability, self-rated health, employment status, age category (for cervical cancer screening), and gender (for fecal occult blood testing). Methods: We linked multiple data sources for this study, including the Canadian Community Health Survey and provincial-level health databases. Using administrative data as our gold standard, we calculated validity measures for self-report (i.e. sensitivity, specificity, positive and negative likelihood ratios, positive and negative predictive values), calculated report-to-record ratios, and conducted a multivariable regression analysis to determine which characteristics were independently associated with over-reporting of screening. Results: Specificity was less than 70% overall and for all subgroups for cervical and breast cancer screening, and sensitivity was lower than 80% overall and for all subgroups for fecal occult blood testing FOBT. Report-to-record ratios were persistently significantly greater than 1 across all cancer screening types, highest for the FOBT group: 1.246 [1.189-1.306]. Regression analyses showed no consistent patterns, but sociodemographic characteristics were associated with over-reporting for each screening type. Conclusions: We have found that in Ontario, as in other jurisdictions, there is a pervasive tendency for people to over-report their cancer screening histories. Sociodemographic status also appears to influence over-reporting. Public health practitioners and policymakers need to be aware of the limitations of self-report and adjust their methods and interpretations accordingly.
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Background
Screening for cervical, breast and colorectal cancer
(CRC) using the Papanicolaou (Pap) test,
mammography, and the fecal occult blood test (FOBT)
respectively are commonly accepted practices in primary care
in Canada. Because of the effectiveness of the Pap test
and its widespread use, Canada currently has one of the
worlds lowest annual incidence and mortality rates for
invasive cervical cancer [1-3]. Mammography is
associated with significant reductions in the relative risk of
death from breast cancer and has long been
recommended by the Canadian Task Force on Preventive
Health Care [4]. Colorectal screening rates in Canada
are currently low, but it has been estimated that if 70%
of the eligible population participated in screening,
mortality due to CRC could drop by 13-15% [5].
Despite the known benefits of screening, the literature
suggests that people who are members of certain
sociodemographic groups are subject to cancer screening
inequities, particularly ethnoracial minorities,
immigrants, people with low levels of education, people with
complex medical conditions, and those of low income
[6-12]. The benefits of screening combined with the
apparent inequalities in screening based on social
disadvantage demonstrate the need for valid methods of
determining and monitoring screening rates. It is therefore
concerning to consider that self-report, a commonly used
method for determining screening history, may have
validity issues and that people from certain sociodemographic
groups might be more likely to inaccurately report cancer
screening than their peers [13-16]. Under-estimating
screening prevalence or over-estimating screening
inequalities could lead to wasted resources, and conversely,
over-estimating screening prevalence or under-estimating
screening inequalities could lead to missed opportunities
for improving screening. Self-report is potentially
vulnerable to acquiescence bias (the tendency to give positive
responses to questions when in doubt) and social
desirability bias (the tendency to respond in a manner that
respondents believe will be viewed favourably), and both
types of bias may be more common among socially
disadvantaged groups [14,16,17].
Literature from the US suggests that these biases in
self-report might exist differentially, and that Hispanics
and African-Americans may be more likely to
overreport screening [14,15]. However, little is known about
the validity of self-report of cancer screening in Canadian
populations or among particular Canadian
sociodemographic groups. Therefore, the objectives of this study
were: i) to determine the validity (...truncated)