Comparison of surrogate with self-respondents regarding medical history and prior medication use

Loren Lipwortha,c, Jon P Fryzeka,c, C Michael Foredb, William J Blota,c and Joseph K McLaughlina,c

a International Epidemiology Institute, Rockville, MD 20850, USA.
b Department of Medical Epidemiology, Karolinska Institute, S-171 77 Stockholm, Sweden.
c Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, Nashville, TN 37232, USA.

Correspondence: International Epidemiology Institute, 1455 Research Blvd, Suite 550, Rockville, MD 20850, USA. E-mail: loren3{at}earthlink.net

Abstract

Background The self-report of medical history and medication use is a common feature of epidemiological research.

Methods In a unique re-interview study, we evaluated the concordance of medical conditions and past medication use reported in two similar interviews 5 years apart.

Results In 196 re-interviews with the subjects themselves, and in 107 with next-of-kin of subjects who died after the first interview, agreement was good or excellent (kappa >=0.40) for 90% (9/10) of the conditions asked about in the personal medical history for both next-of-kin and self-respondents. Agreement was excellent (kappa >0.75) for two conditions, high blood pressure and hysterectomy, among self-respondents. Self- and surrogate respondents also showed similar reproducibility for prescription medications, but next-of-kin respondents tended to have poor agreement (kappa <0.40) for over-the-counter (OTC) medications such as antacids, antihistamines, and analgesics. Next-of-kin also less reliably reported a family history of cancer. When analyses were stratified by type of surrogate respondent, concordance between the two interviews was generally higher for spouses than for other surrogate respondents.

Conclusions This research demonstrates that personal medical history and prescription medication use may be as reliably reported by next-of-kin as self-respondents, but suggests that additional information may be needed to validate measures of OTC medication use and family history of cancer for next-of-kin respondents, possibly through the review of hospital records.

Keywords Self-respondents, next-of-kin, medication use, medical conditions

Accepted 10 July 2000

Epidemiological studies of medical history and past medication use have increasingly relied on interview data obtained through questionnaires administered to patients themselves or to surrogate respondents for seriously ill or deceased individuals. While it has been reported that next-of-kin generally provide accurate data with respect to certain lifestyle factors such as tobacco or alcohol consumption,13 the reliability of medical history data collected by this method has not been adequately investigated. A number of factors have been shown to affect the accuracy of recall of medical information, among them the severity of the condition, the interval between the illness and the interview, and whether or not the illness required hospitalization or a physician's visit.46

The accuracy of medical history data obtained through interview has been assessed by comparing patient responses to information in medical or pharmacy records,712 particularly with respect to oral contraceptive and menopausal oestrogen use. Only a limited number of studies, however, have evaluated the reliability of the interview data by repeating the interview at a later date.1315 In a unique re-interview study, we have evaluated the concordance of reports of medical conditions and past medication use by comparing an original 1980 interview to a 1985 interview. Some of the 1985 interviews involved repeat interviews with the study subjects and some involved interviews with next-of-kin for subjects who died subsequent to the 1980 interview. Thus, self-self (SS) and self-next-of-kin (SN) reproducibility could be compared. Results regarding the reliability or concordance of reporting for cigarette, coffee and alcohol consumption, as well as occupational history, have been presented elsewhere.3,16

Methods

A population-based case-control study was conducted in the Minneapolis-St Paul metropolitan area during 1980 to evaluate potential risk factors for renal cancer.17,18 Cases were white residents of the Minneapolis-St Paul metropolitan area, aged 30–79 years, newly diagnosed with renal cell cancer or renal pelvis cancer between 1974 and 1979. Population-based controls aged 30–64 years were identified from an age- and sex- stratified random sample generated from a complete listing of all telephone subscribers in the study area. An age- and sex- stratified random sample of controls aged 65–80 years was obtained from the Health Care Financing Administration. A total of 586 eligible cases and 714 eligible controls were identified. Of these, 569 cases (97%) and 697 controls (98%) agreed to participate. In-person interviews using a structured questionnaire were conducted to collect data on demographic variables, medication use and medical history, occupational history, tobacco use, diet, beverage consumption, and other factors thought to be related to renal cancer. A more detailed description of the study methods has been published previously.17,18

In 1985, surrogate interviews were sought for all subjects (both cases and controls) who had died, as ascertained through Minnesota state death records, since the initial interview in 1980. Next-of-kin were identified from the death certificates of the original study participants. Spouses were the first choice for surrogate interview, followed by children, then siblings, and then other relatives. Interviews were also sought for a random sample of 100 cases and 100 controls, balanced on sex, who were still alive in 1985, to evaluate the reliability of their responses and to be used as a comparison group. The re-interviews conducted in 1985 were administered in the same manner as in 1980, using the same field procedures, personnel and data preparation and processing methods. The same questionnaire was used in the re-interview, with only the time frame altered so that questions referred to the same calendar period as did the original 1980 interview.

The questionnaire ascertained information about use of the following medications: antibiotics, antihistamines, diuretics, blood pressure medications, diet pills/amphetamines, antacids, menopausal oestrogens, oral contraceptives and analgesics. With respect to analgesic medications, ever use was defined as use 10 times or more during adulthood. For ever users of analgesic drugs, further information was sought on the usual frequency of consumption (days per month) and the length of time (months) at reported level of consumption. For all other types of medication, use was defined as use on a daily basis for 3 months or longer.

With respect to personal medical history, subjects were asked about diagnosis of the following conditions: heart attack, high blood pressure, stroke, diabetes, high cholesterol, prostatitis, bladder infection, kidney infection, kidney stones, and hysterectomy. Regarding family medical history, subjects were asked about the total number of family members (excluding self) who ever had cancer, their relationship to the subject, and the type of cancer they had.

Per cent agreement between 1980 and 1985 responses was calculated by dividing the number of individuals with positive or negative responses regarding a particular drug or medical condition in both the 1980 and 1985 interviews, by the total number of individuals who indicated that they had or had not, respectively, used the medication or had a history of the medical condition in either the 1980 or the 1985 interview. In addition, the kappa statistic was calculated to compare the overall percentage of agreement between dichotomous responses in the 1980 and 1985 interviews.19 Per cent agreement and kappas were computed for both SS and SN pairs of interviews and for cases and controls separately as well as combined. For the main SN analyses, per cent agreement and kappas were computed for all next-of-kin respondents combined; supplementary analyses were conducted by type of surrogate respondent for those comparisons which did not have a ‘0’ in any cell and also had at least 10 ‘yes’ responses for the two interviews. Landis and Koch20 have classified kappa values into three groups with respect to the degree of chance-adjusted agreement. A kappa statistic less than 0.40 is considered to represent poor agreement, between 0.40 and 0.75 fair to good agreement, and greater than 0.75 excellent agreement. Mean values for frequency and duration of analgesic use were compared using the Wilcoxon signed rank test.

Results

A total of 110 study subjects died following the 1980 interview. In 1985, interviews were conducted with next-of-kin of 107 of the deceased subjects (68 cases, 39 controls), as well as with 196 (99 cases, 97 controls) of the 200 living subjects in the comparison sample. Forty-nine per cent of the surrogates were spouses, while 29% were children, 12% were siblings and 10% were other relatives (grandchild, daughter- or son-in-law, stepchild, niece, nephew). In 1985, the mean age of the living subjects was 71 years. In all, 57% of the interviewees in both the 1980 and the 1985 interviews were males. The average interval between the death of a study subject and the surrogate interview was 2.6 years.

Table 1Go shows percentages of exact agreement between original and re-interview SS and SN responses for selected medication use. Since agreement patterns did not differ markedly according to the case-control status of the subject in 1980, only the combined results are presented. With the exception of analgesics, non-use was generally much more common than use, and concordance for both SS and SN interviews was substantially higher for non-use than for use of all drugs. Changes between the two interviews from user to non-user were more frequent than changes from non-user to user. The highest kappa values were observed for menopausal oestrogen and oral contraceptive use among SS interviews (kappa = 0.86 and 0.78, respectively). For the majority of the study medications, the repeatability for SS and SN interviews was remarkably similar, with kappas ranging from 0.42 to 0.71 and indicating good agreement. For antihistamines, antacids and analgesics, however, concordance between the 1980 and 1985 interviews was considerably worse among SN than among SS interviews, with kappas for surrogates ranging from 0.10 to 0.24.


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Table 1 Per cent of exact agreement and kappa values for selected medication use between 1980 interview and 1985 re-interview by type of respondent
 
With respect to analgesic use, surrogate respondents tended to report greater consumption, as measured by either days per month or total number of months, in the 1985 interview than the study subjects themselves reported in the 1980 interview, although the differences were not statistically significant (Table 1Go). For instance, surrogate respondents reported 16.5 days per month of analgesic use in 1985 compared with 12.0 reported by the original study subjects in 1980. Self-respondents showed higher reproducibility, reporting average analgesic use of 8.7 days per month in 1985 compared with 8.2 days per month in the 1980 interview.

Comparisons of responses on personal medical history are presented in Table 2Go. Again, the results for cases and controls were generally similar and have been combined. For personal medical history, there did not appear to be a consistent pattern regarding the reproducibility between SS and SN interviews. Repeatability in identifying a positive history of heart attack, stroke, prostatitis, kidney infection and kidney stones was similar for SS and SN interviews, with most of the kappas in the good range (kappa = 0.40–0.75). In contrast, for high blood pressure, high cholesterol, bladder infection, and hysterectomy, kappas were considerably higher for SS than SN interviews. In fact, among self-respondents, the kappa values for high blood pressure and hysterectomy were in the excellent range (kappa = 0.79 and 0.87, respectively), while the kappa value for high cholesterol among surrogate respondents indicated poor agreement (kappa = 0.10). For diabetes, however, reproducibility was greater in the SN than SS interviews. In analyses stratified by case versus control status, there was no consistent agreement pattern according to whether the subject was a case or a control in the original interview. In particular, for several medical conditions the kappa values were higher for cases than for controls (heart attack among self-respondents, kidney stones and hysterectomy among surrogate respondents), while for other conditions the reverse was true (high cholesterol and kidney stones among self-respondents, heart attack among surrogate respondents) (data not shown).


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Table 2 Per cent of exact agreement and kappa values for personal medical history between 1980 interview and 1985 re-interview by type of respondent
 
In Table 3Go, percentages of exact agreement between original and re-interview responses for variables related to family history of cancer are presented, combined for cases and controls. Overall, next-of-kin respondents were notably less reliable than self-respondents in identifying a positive family history, as characterized by either the total number of family members who ever had cancer, their relationship to the subject, or the type of cancer they had. In fact, among SN interviews, four (40%) of the kappa values were below 0.40, indicating poor or fair agreement. In comparison, for SS interviews, all kappa values were in the good or excellent range, with five of them (50%) being above 0.70.


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Table 3 Per cent of exact agreement and kappa values for family medical history between 1980 interview and 1985 re-interview by type of respondent
 
Table 4Go presents percentages of exact agreement between original and re-interview SN responses, stratified by type of surrogate respondent (spouse versus other), for those comparisons which had adequate numbers. With respect to the selected medication use and medical history variables, concordance between the two interviews was generally higher among spouses than among other next-of-kin respondents. While spouses were not more likely than other surrogates to identify past use of antacids and analgesics, they were considerably more reliable in identifying past use of blood pressure medications and history of high blood pressure.


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Table 4 Per cent of exact agreement and kappa values for medication use and medical history between 1980 interview and 1985 re-interview by type of surrogate respondent
 
Discussion

The findings of the present study indicate that, for history of medication use, surrogate respondents generally provide data that are in good agreement with those provided by the subjects themselves and of similar reproducibility to data obtained in re-interviews with the subjects. Both self- and surrogate respondents typically correctly identified non-use of drugs, suggesting that, as expected, never users and their next-of-kin are particularly confident that they in fact never took the study medication.

There was some indication that next-of-kin respondents could not report use of antihistamines, antacids and analgesics as accurately as they reported use of other types of medications used by the original respondent. This discrepancy likely reflects the fact that use of these particular drugs is mostly over-the-counter (OTC). A complete history of OTC drug use is difficult to obtain reliably under the best of circumstances, and it is especially doubtful whether next-of-kin, particularly those other than spouses, are aware of or can accurately report on such drug exposures.

With respect to personal medical history, agreement was generally good, although no consistent pattern was evident when comparing the accuracy of self- versus surrogate respondents. Repeatability was high in SS interviews for a history of high blood pressure and hysterectomy, and low in SN interviews for a history of high cholesterol in the original subject. Living individuals who were re-interviewed exhibited substantially higher agreement levels than surrogate respondents for each family history variable examined in this analysis. Given that over 75% of surrogate respondents were spouses or children of the original interviewee, this pattern could be due to the fact that some of the cancers in the family, particularly those among parents or grandparents, may have been diagnosed many years earlier, prior to the marriage of the subject or the birth of children. It is also not surprising, again in light of the distribution of surrogate respondents, that, at least among controls, surrogates were able to accurately report history of cancer in a child.

The present study was designed to assess explicitly both subject-to-surrogate and subject-to-subject reproducibility regarding medical history data derived from a community-based case-control interview study. The sample of living subjects who were re-interviewed represents a unique baseline for testing agreement exclusive of the effect of surrogacy. Differences in responses between the original interview and the re-interview cannot be explained by differences in methods of data collection and processing, since the questionnaire, field personnel and procedures, data preparation and reference period for medical history data were the same for both interviews.

It is somewhat surprising that self-respondents who were re-interviewed did not exhibit greater levels of agreement, particularly with respect to seemingly important clinical events such as stroke or diabetes. However, previous studies have demonstrated that the accuracy of recall of past medical events decreases as the interval between the event and the interview becomes longer.13

To our knowledge, only a few studies have attempted to evaluate the reliability of medical history interview data by repeating the interview at a later date.1315 Horwitz and Yu13 interviewed 120 breast cancer patients on two separate occasions and reported excellent agreement for variables such as hysterectomy or family history of breast cancer. More complicated clinical events, such as the removal of ovaries, were remembered less reliably, as was oral oestrogen use occurring many years earlier. Other investigators14,15 have reported excellent reliability in recalling ever use of postmenopausal oestrogens, although details of use, such as dose and starting and stopping dates, were not well-remembered. Longer duration of hormone use was associated with better agreement between two interviews.

In conclusion, it is evident from this analysis that repeatability for general use of medications and personal medical history is generally high for both self- and surrogate respondents. However, our findings also suggest that family history of cancer, as well as detailed information about medical history and drug use (duration of analgesic use, specific type of cancer found in family member), are recalled less accurately by surrogates and may need to be validated through medical record review. Thus, when exposure data are derived from multiple sources, it may be important to stratify results on respondent type in order to examine its influence on the measurement of risk.


KEY MESSAGES

  • Prescription medication use may be as reliably reported by next-of-kin as self-respondents.
  • Reliability of reports of over-the-counter medications such as antacids, antihistamines, and analgesics is, however, lower for next-of-kin respondents.
  • Personal medical history is reliably reported by next-of-kin respondents with the exception of family history of cancer.
  • Additional sources of information, such as medical records appear to be required to validate next-of-kin reports in some but not all instances.

 

References

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