1 Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, CT.
2 Department of Psychiatry, Weill Medical College of Cornell University, White Plains, NY.
3 Department of Psychiatry, Yale University School of Medicine, New Haven, CT, and Northeast Program Evaluation Center, VA Medical Center, West Haven, CT.
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ABSTRACT |
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health surveys; neoplasms; recall; registries
Abbreviations: CI, confidence interval; ECA, Epidemiologic Catchment Area; OR, odds ratio
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INTRODUCTION |
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More recently, self-reported data have been compared with cancer registry records (57
). In a study of persons aged 1574 years, Schrijvers et al. (5
) reported an overall sensitivity of 55 percent (67 percent after excluding cases of nonmelanoma skin cancer). In contrast, a study of elderly persons aged 75 years or more found that only 21 percent of those with a cancer registry record reported a history of cancer (6
). Bergmann et al. (7
) found that the accuracy of self-reported cancer history was quite high among adults participating in a national cancer prevention study (sensitivity estimates ranged from 79 to 93 percent, depending on the definition of "true positive"). Additional studies are needed to assess the validity of self-reported data in epidemiologic investigations (8
). Given the widespread use of self-reports in prevalence estimation and epidemiologic analysis, it is important that we understand better the patterns of inaccurate reporting.
In this study, we compared the self-reported cancer history of participants in a community-based health interview survey with records from the state's cancer registry. Previous studies have shown that individuals tend to underreport rather than overreport cancer history (46
); therefore, the analyses focused on determining the prevalence and correlates of false-negative reporting among the subgroup of participants for whom the tumor registry confirmed a history of cancer. Our study extends the literature by 1) focusing on a community-derived sample of adults with no upper age limit; 2) determining the accuracy of self-reports for cancers diagnosed up to 45 years in the past (compared with 513 years in previous studies); and 3) considering an extensive list of sociodemographic characteristics, cancer-related variables, and health status measures as potential correlates of false-negative reporting.
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MATERIALS AND METHODS |
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As we have described in greater detail elsewhere (11), name and date of birth were used to link ECA and Connecticut Tumor Registry records. The ECA study interviews did not ask respondents their Social Security number, so it could not be used as a matching variable. Exact matches were identified when both name and date of birth corresponded exactly. Potential matches were identified on the basis of matching Soundex (12
) name and satisfying at least two of the following three date-of-birth criteria: 1) exact month of birth, 2) exact day of birth, and 3) ECA's year-of-birth within ±5 years of the Connecticut Tumor Registry's year-of-birth. These criteria were used to account for the possibility of slight discrepancies between ECA and Connecticut Tumor Registry records. Potential matches were visually inspected for plausibility and correctness. In addition, other variables (e.g., sex, address, death certificate number, and year of death/last contact) that were available in both ECA and Connecticut Tumor Registry records were used to help confirm (or disconfirm) the matches. Rigorously confirmed matches were added to exact matches to comprise the analytic sample.
Study sample
We identified 264 of the 5,034 New Haven ECA study respondents as having at least one confirmed cancer diagnosis (except nonmelanoma skin cancer, which is not reported to the Connecticut Tumor Registry) in Connecticut (as opposed to being diagnosed in another state) prior to their baseline ECA study interview. Of the 264 respondents, one had missing data for the self-reported cancer history question; therefore, the sample size for this study was 263 respondents.
Measures
Self-reported cancer history.
During the baseline interview, ECA study respondents were asked the simple screening question, "Have you ever had cancer?" The rate of false-negative reporting was calculated as the percentage of subjects with a registry-confirmed cancer who answered no to this question. Among those with a Connecticut Tumor Registry record of cancer, we were interested in assessing the prevalence and correlates of false-negative reporting of cancer history.
Sociodemographic characteristics.
We considered the following sociodemographic factors in the analysis: sex, race (White or non-White), age (1844, 4564, 6574, 7584, and 85 years), marital status (married, never married, separated/divorced, or widowed), and education (011, 12, and
13 years). Data for these variables came from baseline ECA study interviews.
Cancer-related variables.
We examined the effects of stage at diagnosis, time since diagnosis, treatment history, cancer site, and number of previous cancers on the likelihood of false-negative reporting of cancer history. Data for these variables came from Connecticut Tumor Registry records. Stage at diagnosis was categorized as in situ, localized, regional, or distant, according to the four-level cancer staging system of the Surveillance, Epidemiology, and End Results program (13). Time since cancer diagnosis was defined as the interval between date of cancer diagnosis and date of baseline ECA study interview (<1, 14, 59, 1019, and
20 years). In addition, we assessed the effects of four cancer treatment modalitiessurgery, chemotherapy, radiation, and endocrine therapyon false-negative reporting. Site of cancer was based on the topography codes of the International Classification of Diseases for Oncology, Second Edition (14
). It should be noted that 19 (7.2 percent) of the 263 individuals with Connecticut Tumor Registry records had more than one primary cancer reported to the Connecticut Tumor Registry prior to the ECA study. For these 19 cases, we used the data (on stage at diagnosis, date of diagnosis, treatment history, and cancer site) from their most recent cancer diagnosis.
Health status variables.
Our analysis included four measures of health status: number of physical health conditions, cognitive functioning, self-rated health, and lifetime psychiatric history. Data for these variables came from baseline ECA study interviews. In addition to cancer, ECA study participants were asked whether they had ever had any of the following nine health conditions: 1) hardening of the arteries; 2) high blood pressure or hypertension; 3) heart attack or myocardial infarction; 4) stroke; 5) general neurologic problem or Parkinson's disease; 6) epilepsy, convulsions, or seizures; 7) severe head injury; 8) a series of unexplained falls; and 9) a series of blackouts. The number of positive responses was summed; the summary index had a possible range of 09. Assessed using the Mini-Mental State Examination (15), level of cognitive impairment was categorized as severe (017 points), mild (1823 points), or none (2430 points), based on the number of correct answers out of 30. Respondents' self-reported health status was determined by asking, "At the present time, would you say your health is excellent, good, fair, or poor?" The ECA study used the Diagnostic Interview Schedule (16
) to assess lifetime psychiatric history based on criteria of the Diagnostic and Statistical Manual of Mental Disorders, Third Edition (17
). Lifetime history was assessed for most of the Axis I psychiatric disorders, including affective disorders, anxiety disorders, substance abuse/dependence, and schizophrenic disorders.
Data analysis
Logistic regression modeling (18) was used to identify correlates of false-negative reporting of cancer history. The analyses were performed in three steps. First, we calculated unadjusted odds ratios and 95 percent confidence intervals for each of the potential correlates. Second, we conducted a multivariate analysis using the backward elimination strategy; variables that were significant at the 0.05 level were retained in the final model. Third, to the extent that the sample size allowed, we explored cancer site-specific differences in false-negative reporting. All analyses were performed using SAS software (19
).
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RESULTS |
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Table 2 presents the unadjusted associations between cancer-related variables and false-negative reporting of cancer history. As we noted earlier, 19 persons had more than one primary cancer reported to the Connecticut Tumor Registry prior to the ECA study. Only three (15.8 percent) of these 19 individuals gave a false-negative report of their cancer history, while more than 40 percent of those with one previous cancer did so. Cancers diagnosed further in the past were much more likely to be reported as a false-negative, especially those diagnosed 20 or more years prior to the ECA study (66.7 percent). According to available cancer treatment data, persons who had been treated with radiation were significantly less likely to give a false-negative report of their cancer history than were those who had not been treated with radiation (unadjusted OR = 0.23, 95 percent CI: 0.10, 0.51).
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DISCUSSION |
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Before discussing these results and their implications, some limitations of the data should be addressed. First, besides the Connecticut Tumor Registry, New Haven ECA study records were not linked to other state cancer registries. As a result, respondents who may have been diagnosed with cancer in another state (e.g., prior to moving to Connecticut) were not included in these analyses. It is unlikely, however, that cancer reporting patterns differed substantially between persons diagnosed in Connecticut and those diagnosed elsewhere; therefore, the data are not likely to be biased by the exclusion.
Second, the study was limited to focusing on false-negativity (or its complement, sensitivity) of self-reports among those with a Connecticut Tumor Registry record of cancer. Given that data were not available from medical records or other cancer registries, it was not possible to determine with great confidence other screening parameters, such as specificity and positive and negative predictive values. Recent studies, however, have shown that individuals tend to underreport rather than overreport cancer history; specificity and negative predictive value estimates of greater than 90 percent (often approaching 100 percent) have been found (46
). False-negative reporting, which this study addressed, is clearly more of a problem than false-positive reporting.
Third, it is possible that some errors may have occurred when we matched ECA and Connecticut Tumor Registry records. A common unique identifier (e.g., Social Security number) was not available in both databases; therefore, we had to rely on matching Soundex name and date-of-birth criteria, supplemented by other data elements (e.g., sex, address). However, given the rigor of our linkage procedures, we believe the likelihood of error to be very low. Moreover, any errors in matching that may have occurred would not be expected to be differential with respect to self-reported cancer history.
These limitations notwithstanding, our study had at least two major strengths. First, the analytic sample included adults with a positive history of cancer who were participants in a general, community-based health interview survey. Therefore, the results are likely to be generalizable to many other population-based epidemiologic investigations. In contrast, the study by Bergmann et al. (7), which found a sensitivity of 93 percent for any reported cancer, was of participants in a cancer prevention study, a highly selected group that was probably more motivated to accurately report their cancer history.
Second, the three previous studies (57
) that used registry data to validate self-reported history used cancer records that went back only 513 years. Given that the Connecticut Tumor Registry was established in 1935, we had access to about 45 years of cancer history data. This allowed us to examine the accuracy of self-reports for cancers diagnosed much further in the past.
We found that older persons (especially those aged 75 years) were significantly more likely to give a false-negative report of their cancer history than were middle-aged respondents (those aged 4564 years). This age effect probably reflects a number of different factors. One possibility is that cognitive deficits associated with dementia may result in inaccurate reporting. However, the lack of association between Mini-Mental State Examination score and false-negative reporting suggests that this is not the primary mechanism. For some, cancer may be a "taboo" subject (20
); fear and stigma associated with cancer may make it difficult for some individuals (particularly among the elderly) to acknowledge and discuss their diagnosis. Still others may not have even been aware of their cancer diagnosis, either because of decreased desire to be informed about their disease status or as a result of poor patient-physician communication relative to other age groups (21
). Communication with elderly patients may be adversely influenced by such factors as cognitive and sensory impairments, multiple acute and chronic conditions, and paternalistic attitudes on the part of physicians (22
24
).
Independent of age, these data showed that cancers diagnosed further in the past (especially 20 years ago) were more likely to be underreported. Accuracy of recall often decreases with time since event or exposure (25
). Some respondents may have felt that cancers diagnosed years and decades ago were unimportant and not worth reporting, since they had survived and moved on. Alternatively, the observed association between time since diagnosis and self-reported cancer history may reflect a period effect with respect to patient-physician communication and disclosure of cancer diagnosis; evidence suggests that, in many instances, cancer diagnoses were not communicated clearly, if at all, in the past, but over time, patient-physician communication has improved (24
).
Non-White respondents were significantly more likely to underreport their cancer history than were White respondents, even after controlling for age, education, and other factors. Several explanations for this observed association are possible. First, it may be that non-White persons were less likely to have had a history of more accurately reported cancers (e.g., skin and breast cancers). The small sample size of non-White respondents precluded our performing the detailed analyses by race needed to test this hypothesis. Second, non-White respondents may have been less informed about their cancer diagnosis as a result of racial differences in patient-physician interaction and communication (26, 27
), including failure to use culturally appropriate language when discussing cancer (28
). Third, there is considerable mistrust of health care professionals and researchers among minority groups, especially the Black population (29
); mistrust of study interviewers could have resulted in greater false-negative reporting by non-White respondents.
We found that respondents who had a history of more than one primary cancer were less likely to give a false-negative report of their cancer history than were those who had had one episode of cancer prior to the ECA study. This result probably reflects the fact that persons with a more extensive cancer history are better able to recall their history. Less clear were the findings that respondents with a Connecticut Tumor Registry record of radiation treatment were less likely to underreport their cancer history than were those with no such record and that no other treatment modalities were similarly associated with false-negative reporting. While interventions such as surgery are routinely used to treat a variety of conditions in addition to cancer, it may be that radiation therapy is more uniquely associated with treatment of cancer and, therefore, serves as a better memory trigger.
Rate of false-negative reporting varied widely by cancer site; however, the limited sample size prevented detailed site-specific analyses. Consistent with other studies (47
), our study found that breast cancer was among the most accurately reported cancers. This may, in part, be attributed to greater public awareness and destigmatization of breast cancer and the fact that it can profoundly influence one's self-identity and body image. Moreover, evidence suggests that breast cancer is more frequently disclosed and discussed with patients than are other forms of cancer (30
, 31
). The high rates of false-negative reporting found for cancers of the central nervous system and bone marrow may reflect the fact that respondents were unaware that diagnoses such as meningioma, leukemia, and myeloma are indeed "cancer" diagnoses. In addition, such cancers do not present with the obvious visual and tactile cues associated with soft tissue and skin tumors.
Most of the cancers in this study were diagnosed in the 1970s. Although it is generally true that societal attitudes toward cancer and patient-physician communication have improved over time, the extent to which these changes translate into more valid self-reports is unclear. A repetition of our study using more recent cancers would be valuable. While we would probably expect the overall rate of false-negative reporting to be somewhat lower in future cohorts, it remains to be seen whether the validity of self-reported history continues to differ by sociodemographic and cancer-related factors.
These results suggest that epidemiologic studies that rely on self-reported cancer history may be biased. Cancer prevalence rates based on self-reported data will be underestimated, particularly for vulnerable populations such as the elderly and non-Whites. Control of confounding (either by sample restriction or through statistical analysis) will be incomplete. The errors are likely to be differential across sociodemographic subgroups and cancer diagnoses. From a public health policy perspective, underestimation of cancer prevalence may lead to inappropriate funding decisions.
In practical terms, these findings suggest improving the methods used to assess cancer history in epidemiologic studies. For studies in which cancer history is a primary focus, self-reported data may be inadequate without validation of the quality of the information collected, ideally by comparing self-reported history with cancer registry and/or medical records. For studies in which cancer history will be used as a covariate or as part of an aggregate measure of medical status, a reasonable approach may be to modify questionnaires to improve respondents' understanding and recall. For example, given that some false-negative reporting may be attributed to misinterpreting or misunderstanding the term "cancer," it may be helpful to include follow-up or probe questions that use alternative words, such as "tumor" and "malignancy," to elicit cancer history. Probe questions asking respondents about major medical procedures (e.g., radiation treatment, chemotherapy, surgery) and hospital inpatient stays also could serve as memory triggers.
In conclusion, using tumor registry records to validate self-reported data, we found that a typical question asking respondents about their cancer history had low sensitivity. The rate of false-negative reporting varied by age, race, number of previous tumors, the time since cancer diagnosis, treatment history, and cancer site. Future research is needed to investigate whether the use of probe questions and memory triggers can improve the validity of self-reported cancer history.
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ACKNOWLEDGMENTS |
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NOTES |
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REFERENCES |
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