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PubMed2005

The role of proxy information in missing data analysis.

This article investigates the role of proxy data in dealing with the common problem of missing data in clinical trials using repeated measures designs. In an effort to avoid the missing data situation, some proxy information can be gathered. The question is how to treat proxy information, that is, is it always better to utilize proxy information when there are missing data? A model for repeated measures data with missing values is considered and a strategy for utilizing proxy information is developed. Then, simulations are used to compare the power of a test using proxy to simply utilizing all available data. It is concluded that using proxy information can be a useful alternative when such information is available. The implications for various clinical designs are also considered and a data collection strategy for efficiently estimating parameters is suggested.

Canada↗

PubMed2001

A messy necessary end: Health care proxies need our support.

OBJECTIVE: To promote development of written advance directives and appointment of a proxy for health care by patients who are under the care of a neurologist. BACKGROUND: since 1989, the American Academy of Neurology (AAN) has endorsed but not actively promoted advance directives. In the years since publication of the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatment (SUPPORT), much published material has contradicted the notion that creating advance directives offers patients a useful means of extending their autonomy. METHODS: The author reviewed the post-SUPPORT literature, in which numerous articles criticize and others continue to uphold the use of advance directives. He also conducted a pilot study concerning the health care proxy. Additionally, he reexamined his experiences as an ethics consultant, mindful of the medical literature unfavorable to advance directives, to challenge his own opinion that creating directives and appointing a health care proxy are valuable activities for all adults to engage in and for neurologists to promote. RESULTS: Very few articles focus on advance directives and neurology. This literature is not present in neurology specialty journals. Only two of the five neurologists approached by the author were positive about advance directives and collaborated fully in the pilot study. Reviewing his experiences provided the author with numerous examples of the actual or potential usefulness of health care proxies. CONCLUSIONS: Increasing the advance directives literature in neurology specialty journals may lead to the creation of health care documents by more neurologic patients and the development of innovative ways of extending the autonomy of previously competent individuals. The author has recently formed a volunteer organization, Patient Advocates to Preserve Autonomy (PAPA), to increase effectiveness of advance directives. It is hoped that the reservations of some neurologists about advance directives and proxy decision-making may be lessened if they improve their knowledge of the subject and convince themselves that addressing it is one of the obligations attendant on providing "principal care" for many of their patients. The focus initially needs to be on attitudes, rather than methods. However, this pilot project showed that a passive approach is ineffective. A campaign within the AAN to promote advance directives as an aspect of principal care would be helpful. Patients who have lost the capacity to make their own health care decisions often benefit from advance directives and, especially, from having an appointed health care proxy. Those benefits may improve if patient, proxy, and physician are carefully prepared for their roles.

Advance Directives↗

PubMed2000

A comparison of primary and proxy respondent reports of habitual physical activity, using kappa statistics and log-linear models.

BACKGROUND: Many epidemiological studies rely in part on proxy informants. There is little published information on the reliability of proxy-respondent reports of physical activity. METHODS: Self-reported data on vigorous and moderate physical activity, from a representative sub-sample of participants in a community-based case-control study of coronary heart disease, were compared with information collected from their next-of-kin. RESULTS: Relative to primary respondents, proxy respondents under-reported activity by approximately 10 percentage points, for both leisure and work-time activity. On a simple three point scale (inactivity/moderate activity/physical activity), 70% of primary-proxy pairs were in exact agreement with regard to leisure time activity and 67% of pairs were in exact agreement on work-time activity. The corresponding values for the weighted kappa statistic were 0.66 [95% confidence interval (CI) 0.59-0.72] and 0.62 (0.54-0.72). Log-linear modelling provided evidence for superior agreement on worktime activity when the proxy was not the primary respondent's spouse. DISCUSSION: Overall levels of primary-proxy respondent agreement on physical activity seem somewhat lower than has been reported for smoking and alcohol-drinking frequency. There seems little reason to prefer spouse proxies when endeavouring to elicit information on work-time physical activity. Log-linear modelling provides an efficient means of exploring covariate effects in observer-agreement studies.

Adult↗

PubMed2000

Proxy reporting in the National Population Health Survey.

OBJECTIVES: This article examines the extent of proxy reporting in the National Population Health Survey (NPHS). It also explores associations between proxy reporting status and the prevalence of selected health problems, and investigates the relationship between changes in proxy reporting status and two-year incidence of health problems. DATA SOURCE: Cross-sectional results are based on the 1996/97 NPHS Health file and General file. Longitudinal results are based on 1994/95 respondents who were still residing in households in 1996/97. ANALYTICAL TECHNIQUES: The extent of proxy reporting in the various NPHS files was computed. Prevalence estimates of selected health problems from the two 1996/97 cross-sectional files were compared. Multivariate analyses were used to estimate associations between proxy reporting status and health problems. MAIN RESULTS: For several health conditions, prevalence estimates based on the 1996/97 cross-sectional Health file (where proxy reporting was less common) were significantly higher than estimates derived from the General file. Individuals whose data were proxy-reported in 1994/95 and self-reported in 1996/97 had higher odds of reporting new cases of certain health conditions.

Adolescent↗

PubMed1998

First, do no harm: the use of covert video surveillance to detect Munchausen Syndrome by Proxy--an unethical means of "preventing" child abuse.

Since it was first identified in 1977, Munchausen Syndrome by Proxy has uniquely affected the way in which the medical and legal communities deal with the issue of child abuse. Inherent in the medical response to the disease are issues of suspicion, investigation, identification, confrontation, and, of course, the health of an innocent child. Given the deceptive dynamics of this disease, however, denial and disbelief naturally overshadow every action taken by medical professionals in pursuing these issues. Fortunately, as medical knowledge about the dynamics of the disease continues to develop, medical professionals become more willing and better able to identify the disease and focus their response on the safety of the child. The greatest problem in prosecuting Munchausen Syndrome by Proxy is that judges and juries remain unwilling to accept the reality of the disease. Consequently, in an effort to confirm medical suspicions and quell legal doubts, the medical community has resorted to covert video surveillance of the abuse while it is being perpetrated in the hospital. In this Article, Flannery argues that this response is an unnecessary and unethical, means of preventing Munchausen Syndrome by Proxy and protecting the child. Flannery supports the approach taken by the Family Court of New York in addressing Munchausen Syndrome by Proxy cases. The Family Court of New York recognizes the unique dynamics of this bizarre disorder, and, therefore, considers all cumulative circumstantial evidence in a Munchausen Syndrome by Proxy case, comparing the facts of the subject case to the commonly accepted features of confirmed cases. Part of the circumstantial evidence that should be considered, Flannery argues, is the dissipation of the child's condition upon temporary separation from the alleged perpetrating parent. As is done by the Flannery Court of New York, a res ipsa loquitur standard should then be applied, and an appropriate disposition for the child should be determined. By employing this standard, the court may confirm suspicions of Munchausen Syndrome by Proxy while avoiding the unnecessary harm to the child inherent in the covert video surveillance of Munchausen Syndrome by Proxy.

Child↗

PubMed2006

Utility of proxy versus index respondent information in a population-based case-control study of rapidly fatal cancers.

PURPOSE: This work provides an empirical assessment of the usefulness of obtaining exposure data from proxy respondents. METHODS: Two independent case groups were formed in data from a population-based case-control study. One case set was derived from proxy respondents. The second case series was derived from respondents who self-reported. The second case group was matched to the proxy case group for age, cancer site, and sex. These data were compared with a control group for completeness of information and identifying heterogeneity of risk estimates for a variety of variables. Index cases and controls were matched to the 829 available proxy respondents for sex, age (5-year groups), and cancer site. RESULTS: Proxy respondents provided levels of complete information similar to index cases and controls for height and weight; occupational physical activity; consumption of coffee, alcohol, and cigarettes; and family history of cancer. Proxies had more missing responses for variables concerning recreational physical activity, clinical depression, age at first menstruation, use of oral contraceptives, and occupational exposure to pesticides. Polytomous logistic regression models found only a few examples of meaningful heterogeneity among all variables, limited to models for coffee consumption and cigarette smoking. CONCLUSIONS: Our data suggest that proxy respondents, especially parents and spouses, provide adequately complete information for many, but not all, exposures common in epidemiologic studies.

Adult↗

PubMed1998

Comparison of patient and proxy EORTC QLQ-C30 ratings in assessing the quality of life of cancer patients.

The aim of this study was to examine whether significant others can provide useful proxy information on the health-related quality of life (QL) of cancer patients. We examined the level and pattern of agreement between patient and proxy ratings of the EORTC QLQ-C30, the reliability and validity of both types of information, and the influence of several factors on the extent of agreement. QL ratings were obtained for 307 and 224 patient-proxy pairs (at baseline and follow-up, respectively). Agreement was moderate to good (ICC = 0.42 to 0.79). Multitrait-multimethod analysis showed good convergence and discrimination of specific QL domains. Comparison of mean scores revealed a small but systematic bias between patient and proxy ratings. The maximum level of disagreement was found at intermediate levels of QL, with smaller discrepancies noted for patients with either a relatively poor or good QL. Both patient and proxy QL ratings were reliable and responsive to changes over time. Several characteristics of the patients and their significant others were found to be associated with the level of agreement, but explained less than 15% of the variance in patient-proxy differences. In conclusion, the present findings lend support to the viability of employing significant others as proxy respondents of cancer patients' quality of life where this is necessary.

Adult↗

PubMed1990

Reliability of proxy response on mental health indices for aged, community-dwelling women.

The correspondence between respondent and proxy response was evaluated on 4 mental health measures (Affect Balance Scale, Center for Epidemiological Studies Depression Scale, Mental Status Questionnaire, and Mini-Mental State Examination) with a sample of 538 respondent-proxy pairs. Results indicated that respondent and proxy responses were strongly associated, particularly for the cognitive measures. This association was found even for respondents classified as depressed or cognitively impaired. Although there was evidence of proxy bias, with proxies underrating affective status and overrating cognitive status, the magnitude of the bias proved small for all scales but the Mental Status Questionnaire. Examination of response comparability by proxy characteristics showed that choice of proxy affected agreement and bias. Implications of these findings for survey research are discussed.

Aged↗

PubMed1996

Use of proxies to measure health and functional status in epidemiologic studies of community-dwelling women aged 65 years and older.

Proxy and subject responses to survey questions about chronic conditions, health symptoms, and physical and instrumental functioning were compared to determine the extent of disagreement, the direction of nonrandom discrepancies (i.e., bias), and how disagreement and bias vary by proxy and subject characteristics. Subjects included 538 community-dwelling women aged 65 years and older who participated in the third home interview of a health survey in Baltimore, Maryland, 1986, and a self-designated proxy for each. The authors observed kappa values of > 0.6 (i.e., substantial to almost perfect agreement) for five of nine chronic conditions, no health symptoms, six of seven physical tasks of daily living, and seven of seven instrumental tasks of daily living. With few exceptions, proxies were more likely than subjects to report the presence of a condition, symptom, or functional problem. Variations in agreement and bias were noted by subject and proxy characteristics, with different patterns observed for different measurement areas. When using proxy reports in place of self-reports, it is important to evaluate the impact that using proxies has on study results.

Activities of Daily Living↗

PubMed1997

Proxy reporting in five areas of functional status. Comparison with self-reports and observations of performance.

Proxy ratings of functional status were compared with subject self-reports in five domains relevant to the study of older persons and with observations of subject performance in two areas (physical and instrumental functioning). Data were derived from 233 proxy-subject pairs evaluated in a prospective study of hip fracture patients aged 65 years or more in Baltimore, Maryland (1990-1991). Agreement between proxy and subject reports was highest for a summary measure of instrumental functioning and lowest for a measure of depression. Proxies tended to report more disability than did subjects, although bias varied by function. Patterns of agreement for proxy reports versus observations of performance compared with patterns for proxy reports versus subject reports were lower for measures of instrumental functioning, and bias was generally more extreme for instrumental and physical functioning measures. The authors conclude that agreement and bias differ by functional domain, by the way summary measures are created and scored, and by the criterion against which proxy reports are compared.

Activities of Daily Living↗

PubMed1986

The use of proxies in health surveys. Substantive and policy implications.

It has traditionally been assumed that obtaining health and illness behavior data by proxy on household members who are not present during the actual interview presents no significant threats to the internal validity of subsequent analyses. Using data on the 78,439 adults interviewed in person or by proxy (about 37% of the total adult sample) as part of the 1978 Health Interview Survey, the authors examine whether the use of proxy respondents alters the results of empirical assessments of the behavioral model of health services utilization or the policy implications that can be derived from it. Two important findings emerge from these analyses. On the one hand, failing to consider explicitly the possibility of a proxy effect (i.e., including a proxy variable in the analyses) does not alter the effect parameters estimated for the behavioral model. On the other hand, failing to consider explicitly the effect of using proxies appears to underestimate slightly physician and hospital contact rates (by 4% and 2%, respectively), as well as the volume of physician utilization. The substantive and policy implications of these findings are discussed, as are two alternative explanations that suggest that proxy-respondents simply use fewer health services either because they are "too busy" or because they are in slightly better health.

Adult↗

PubMed1989

The use of female spouse proxies in common symptom reporting.

To determine the quality of proxy health reports by telephone the 1984 Wisconsin Health Status Survey employed a repeated-measure design in an interview covering 22 recently occurring health and psychologic complaints. Comparisons on individuals in households containing two or more adults revealed a relatively weak correspondence between the respondent and proxy reports. While a previous analysis of these data found that certain characteristics thought to underlie reporting differences are not useful in explaining proxy underreporting, the current analysis focuses on spousal pairs and achieves greater success by applying somewhat more sophisticated methods. The authors examined the nature, persistence, and number of health complaints as factors in reporting bias. They find evidence that female proxies vary by symptom in their ability to report common complaints and also observed that proxy underreporting diminishes somewhat as the persistence of symptoms increases. Using multiplicative models, the authors show that the gross misclassification of complaints is concentrated in the respondent-proxy pairs with the shortest exposure to the symptom. Finally, an examination of the disagreements on all 22 health complaints simultaneously revealed that neither mutual misallocation by respondents and proxies nor a diminished health status of the individual reported on are important influences on reporting behavior.

Female↗

PubMed2002

Proxy validation of patient self-reports of ADL and IADL function before and after electroconvulsive therapy.

OBJECTIVE: To determine whether electroconvulsive therapy (ECT) patients' self-reported functional status is similar to that reported by a proxy. BACKGROUND: Increasing levels of depression are associated with deteriorating functional status as reflected in the Instrumental Activities of Daily Living (IADL) scale. Depressed patients referred for ECT have poorer IADL status compared with depressed patients receiving medications, suggesting that IADL status may shape physicians' decision to recommend ECT ( 1). Further, IADL status improves with treatment of depression, both in ECT-and medication-treated patients. Given the potential importance of IADL status for ECT patients, we examined whether IADL status as reported by patients prior to ECT was comparable to IADL status as described by a proxy. DESIGN/METHODS: Forty depressed patients (23 men and 17 women, mean age 58.1 +/- 17.5) were each interviewed alone with the 21-item Hamilton Depression Rating Scale (HDRS), Mini-Mental State Exam (MMSE), an Activities of Daily Living (ADL) scale, and an IADL scale. We then privately interviewed a first-degree relative who lived with each patient and recorded their impression of the patient's ADL and IADL function before ECT, and at 2 and 4 weeks after ECT. RESULTS: baseline scores for HDRS and MMSE were consistent with a severe level of depressive symptoms and intact global cognitive function. Patients' and proxies' IADL scores were highly correlated before ECT, 2 weeks after ECT, and 4 weeks after ECT. Significant, but slightly weaker correlations were seen for ADL scores. CONCLUSIONS: Ideally, ADL and IADL function would be measured by direct observation rather than either patient or proxy report. At this time it is unknown whether the patient or the proxy report should be considered the "gold standard." In this study, the patients' self-reported functional scores were highly correlated with the proxies' scores. We conclude that patients' reports of their function are roughly comparable to proxies' impressions before and after ECT.

Activities of Daily Living↗

PubMed2000

Bias in proxies' reports of disability: data from the National Health Interview Survey on disability.

OBJECTIVES: These studies examined whether differences between self-reports and proxy reports of disabilities reflect proxy response biases or only respondent selection factors. METHODS: The data were from the National Health Interview Survey on Disability (1994-1995, phases 1 and 2). In study 1, reports of disabilities were regressed on respondent status, self vs proxy, and demographic factors. In study 2, the ratios of the proportions of self-reports and proxy reports of disabilities were regressed on independent lay ratings of observability of these disabilities and their "interactional" nature. In study 3, the disability reports for people who differed in respondent status in one phase but self-reported the same disability in the other phase were compared. RESULTS: In study 1, proxies under-reported disabilities for people aged 18 to 64 years but overreported for people 65 years or older. In study 2, the observability and interactional scores accounted for more than 60% of the variance of self and proxy differences in an inverse relationship, study 3 confirmed the basic findings of study 1. CONCLUSIONS: Use of proxies in representative surveys on disability introduces systematic biases, affecting national disability estimates.

Activities of Daily Living↗

PubMedDate not supplied

[Hypochondriasis by proxy in children: report of two cases]

OBJECTIVE: To emphasize important aspects for the diagnosis and approach of patients with history of child abuse, related with the Munchausen Syndrome by proxy, and its variant, Hypochondriases by proxy. METHODS: The authors describe two cases followed in the Pediatric Service in a terciary hospital of Salvador, Bahia, in which they found aspects of the medical history and physical examination of these children and in the mothers' behavior compatible with Munchausen by proxy (Factitious disorder by proxy). RESULTS: In the two cases presented, we observed a standard in the clinical history, described as recurrent inpatient and outpatient medical support, through the last three years, without the identification of abnormal results. These facts do not decreased the certainty of the mothers about their children's disease (hypochondriases by proxy). Furthermore we observed cooperation on the part of the children by incorporating the role of the sick one, which made their school and social adaptation more difficult. CONCLUSIONS: The pediatrician must be aware of the diagnosis of Munchausen Syndrome by Proxy and its variation, hypochondriases by proxy, in those cases of unsuitable and recurrent disease, lack of symptoms and signs in the absence of parents, and diagnostic methods with meaningless results. When absolutely certain about diagnosis, the physician must establish the risk for the child (increased mortality in these cases) and suggest psychotherapy for the mother or perpetrator.

Journal Article↗

PubMed2000

[Simultaneous query and retrieve from multiple DICOM image archives using a proxy server].

PURPOSE: DICOM clients could not access more than one archive simultaneously in the previous PACS systems. We developed a proxy server which makes it possible for clients to query and retrieve images from multivendor DICOM archives simultaneously. METHODS: We used a Web server that supports the DICOM query and retrieve(Q/R) service class as a proxy server. This system consisted of two DICOM servers and six DICOM clients of different vendors in the Radiology Department. Through Web browsers on the clients, requests for Q/R were transmitted to the proxy server by hypertext transfer protocol. The proxy server communicated with DICOM servers by DICOM Q/R Service Class(C-FIND, C-MOVE), and then DICOM servers directly transmitted images to DICOM clients by DICOM Storage Service Class(C-STORE). RESULTS: DICOM clients could transmit Q/R requests to two DICOM servers simultaneously via the proxy server and receive requested images promptly. Confirmation of conformance among the proxy server, DICOM archives, and DICOM clients became much easier than previously. CONCLUSION: A Web server working as a proxy server of the DICOM Q/R Service Class is an effective solution for allowing DICOM clients to communicate with multiple DICOM archives.

Computer Communication Networks↗

PubMed2000

The accuracy of proxy ratings of life-style activities using the Adelaide Activities Profile.

The accuracy of proxy ratings with the Adelaide Activities Profile (AAP) has not been previously described. The current study sought to redress this situation by sampling spouses and adult children (the two most plausible classes of proxy), and by selecting healthy community dwelling people aged 65 years and over as index cases. The aim was to examine the level of agreement, and the nature of any disagreement, between index case and proxy AAP ratings. Data were obtained from 87 family units, of which 61 comprised husband, wife and adult child, while 26 consisted of husbands and wives only. Index-proxy agreement for the AAP scales was in general very satisfactory. Wives were more accurate proxies than their husbands, and both were more accurate than their children, although the latter were still adequate. Proxy accuracy was not further enhanced by age, sex, or frequency of contact with index cases.

Aged↗

PubMed2006

Evaluation of male COPD patients' health status by proxies.

BACKGROUND: It is not always possible to collect information about health from patients, so information from proxies (relatives and others) is used to aid medical decision-making, but there has been no formal evaluation of the reliability of their reports. The aim of this study was to analyse the reliability and validity of the St. George's Respiratory Questionnaire (SGRQ) answered by proxies and to determine their accuracy as raters. METHODS: Stable symptomatic male COPD patients and relatives living in the same house independently completed the same version of the SGRQ. RESULTS: Forty-six male patients were studied; age 72.1+/-7.3 years, pre-bronchodilator FEV(1) 37.9+/-14.7% predicted, 30.4% on long-term oxygen therapy. Internal consistency (Cronbach's alpha) was over 0.73 for all domains and >0.9 for the total score. Their scores correlated with dyspnoea (r=0.30-0.45) and FEV(1) (r=0.4-0.61). The proxies could distinguish between levels of disease severity, but with a weaker discriminant power compared to patients. Seventy-two per cent of proxies over-reported the degree of the patient's overall health status impairment, especially at mild-moderate scores. Proxies showed weaker correlations at the more severe scores. CONCLUSIONS: The SGRQ was reliable and valid when administered to relatives of male COPD patients; however due to the systematic over-reporting of the level of the patient's health status impairment, caution should be applied whilst trying to use proxies as surrogates for male COPD patients.

Aged↗