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Response Proportions (response + proportion)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

General Health Status and Changes in Chewing Ability in Older Canadians over Seven Years

JOURNAL OF PUBLIC HEALTH DENTISTRY, Issue 2 2002
David Locker PhD;
Abstract Objectives: The purpose of this study was to describe the onset of and recovery from chewing problems in an older adult population over a seven-year period and to describe factors associated with these changes. Of particular interest was the relationship between general health and changes in oral functioning - Methods: The data came from a longitudinai study of community-dwelling individuals who were aged 50 years and older when first recruited. Data were collected at baseline (n=907) and at three (n=611) and seven-year (n=425) follow-ups. Oral function was assessed by means of a six-item index of chewing ability. Data were weighted to account for loss to follow-up using weights derived from the seven-year response proportions for dentate and edentulous subjects. Logistic regression analysis using backward stepwise selection was used to identify. predictors of onset and recovery. Results: At baseline, 25 percent of subjects reported a problem chewing. This rose to 26 percent at three years and 34 percent at seven years. The seven-year incidence of chewing dysfunction was 19 percent. Of those with a chewing problem at baseline, 21 percent did not have a problem at seven years. A logistic regression model predicting the seven-year incidence of chewing problems indicated that subjects aged 65 years or older, the edentulous, those rating their oral health as poor, those without dental insurance and those without a regular source of dentai care were more likely to be an incident case. In addition, a variable denoting the number of chronic medical conditions at baseline also entered the model. A logistic regression model predicting recovery indicated that older subjects, the edentulous, those from low-income households, and those with limitations in activities of daily living were less likely to recover over the observation period. Conclusion: The results of this study indicate a marked increase in the prevalence of chewing problems in this older adult population over the seven-year observation period. Poorer general health at baseline increased the probability of the onset of a chewing problem and decreased the probability of recovery. [source]

Epidemiologic research on man-made disasters: Strategies and implications of cohort definition for World Trade Center worker and volunteer surveillance program

MOUNT SINAI JOURNAL OF MEDICINE: A JOURNAL OF PERSONALIZED AND TRANSLATIONAL MEDICINE, Issue 2 2008
David A. Savitz PhD
Abstract Studies of long-term health consequences of disasters face unique methodologic challenges. The authors focused on studies of the health of cleanup and recovery workers, who are often poorly enumerated at the outset and difficult to follow over time. Comparison of the experience at the World Trade Center disaster with 4 past incidents of chemical and radiation releases at Seveso, Italy; Bhopal, India; Chernobyl, Ukraine; and Three Mile Island, USA, provided useful contrasts. Each event had methodologic advantages and disadvantages that depended on the nature of the disaster and the availability of records on area residents, and the emergency-response and cleanup protocol. The World Trade Center Worker Monitoring Program has well-defined eligibility criteria but lacks information on the universe of eligible workers to characterize response proportions or the potential for distortion of reported health effects. Nonparticipation may result from lack of interest, lack of awareness of the program, availability of another source of medical care, medical conditions precluding participation, inability to take time off from work, moving out of the area, death, or shift from initially ineligible to eligible status. Some of these considerations suggest selective participation by the sickest individuals, whereas others favor participation by the healthiest. The greatest concern with the validity of inferences regarding elevated health risks relative to external populations is the potential for selective enrollment among those who are affected. If there were a large pool of nonparticipating workers and those who suffered ill health were most motivated to enroll, the rates of disease among participants would be substantially higher than among all those eligible for the program. Future disaster follow-up studies would benefit substantially by having access to accurate estimates of the number of workers and information on the individuals who contributed to the cleanup and recovery effort. Mt Sinai J Med 75:77,87, 2008© 2008 Mount Sinai School of Medicine [source]

A Cautionary Note on Exact Unconditional Inference for a Difference between Two Independent Binomial Proportions

BIOMETRICS, Issue 2 2003
Devan V. Mehrotra
Summary Fisher's exact test for comparing response proportions in a randomized experiment can be overly conservative when the group sizes are small or when the response proportions are close to zero or one. This is primarily because the null distribution of the test statistic becomes too discrete, a partial consequence of the inference being conditional on the total number of responders. Accordingly, exact unconditional procedures have gained in popularity, on the premise that power will increase because the null distribution of the test statistic will presumably be less discrete. However, we caution researchers that a poor choice of test statistic for exact unconditional inference can actually result in a substantially less powerful analysis than Fisher's conditional test. To illustrate, we study a real example and provide exact test size and power results for several competing tests, for both balanced and unbalanced designs. Our results reveal that Fisher's test generally outperforms exact unconditional tests based on using as the test statistic either the observed difference in proportions, or the observed difference divided by its estimated standard error under the alternative hypothesis, the latter for unbalanced designs only. On the other hand, the exact unconditional test based on the observed difference divided by its estimated standard error under the null hypothesis (score statistic) outperforms Fisher's test, and is recommended. Boschloo's test, in which the p-value from Fisher's test is used as the test statistic in an exact unconditional test, is uniformly more powerful than Fisher's test, and is also recommended. [source]