David R. Ragland

Physical Activity and Reduced Occurrence of Non-Insulin-Dependent Diabetes Mellitus

BACKGROUND Physical activity is recommended by physicians to patients with non-insulin-dependent diabetes mellitus (NIDDM), because it increases sensitivity to insulin. Whether physical activity is effective in preventing this disease is not known. METHODS We used questionnaires to examine patterns of physical activity and other personal characteristics in relation to the subsequent development of NIDDM in 5990 male alumni of the University of Pennsylvania. The disease developed in a total of 202 men during 98,524 man-years of follow-up from 1962 to 1976. RESULTS Leisure-time physical activity, expressed in kilocalories expended per week in walking, stair climbing, and sports, was inversely related to the development of NIDDM: The incidence rates declined as energy expenditure increased from less than 500 kcal to 3500 kcal. For each 500-kcal increment in energy expenditure, the age-adjusted risk of NIDDM was reduced by 6 percent (relative risk, 0.94; 95 percent confidence interval, 0.90 to 0.98). This association remained the same when the data were adjusted for obesity, hypertension, and a parental history of diabetes. The association was weaker when we considered weight gain between the time of college attendance and 1962 (relative risk, 0.95; 95 percent confidence interval, 0.90 to 1.00). The protective effect of physical activity was strongest in persons at highest risk for NIDDM, defined as those with a high body-mass index, a history of hypertension, or a parental history of diabetes. These factors, in addition to weight gain since college, were also independent predictors of the disease. CONCLUSIONS Increased physical activity is effective in preventing NIDDM, and the protective benefit is especially pronounced in persons at the highest risk for the disease.

TYPE-A BEHAVIOR AND MORTALITY FROM CORONARY HEART-DISEASE

The relation of behavior (Type A or Type B) to the morbidity and mortality of coronary heart disease (CHD) is still debated. We studied the survival of 257 male patients with CHD from the initial, 8.5-year phase of the Western Collaborative Group Study to see whether behavior type--as assessed by a structured interview before the CHD event--was related to subsequent CHD mortality. Behavior type was not related to mortality in 26 patients who died within 24 hours of the coronary event. However, of the 231 patients who survived for 24 hours, the mortality rate associated with CHD among 160 Type A patients studied during an average 12.7 years was 19.1 per 1000 person-years. This was unexpectedly lower than the corresponding rate of 31.7 among 71 Type B patients who were followed for an average of 11.5 years (P = 0.04). In a proportional-hazards survival analysis, which controlled for variable follow-up time, the type of initial coronary event, and traditional risk variables, the relative CHD-associated mortality rate among Type A as compared with Type B patients was 0.58 (P = 0.03; 95 percent confidence interval, 0.35 to 0.96). The lower mortality among Type A subjects occurred in both younger and older subgroups but was more pronounced in patients whose initial diagnosis was symptomatic myocardial infarction rather than silent myocardial infarction or angina pectoris. This apparent advantage associated with Type A behavior is surprising and needs confirmation, but the results do indicate that patients with CHD and a Type A behavior pattern are not at increased risk for subsequent CHD mortality.

Dichotomizing Continuous Outcome Variables: Dependence of the Magnitude of Association and Statistical Power on the Cutpoint

Dichotomizing a continuous outcome variable casts that variable in traditional epidemiologic terms (that is, disease, no disease). One consequence is overall reduced statistical power. A more fundamental concern is that the magnitude of various measures of association (for example, prevalence ratio, odds ratio) and statistical power depend on the cutpoint used to dichotomize the variable. The phenomenon is illustrated with a hypothetical situation assuming a two-level predictor variable and a normally distributed outcome variable. As the cutpoint is increased from lower to higher values, the prevalence ratio increases steadily, the odds ratio is described by a U-shaped curve, and statistical power is described by an inverted U-shaped curve. Furthermore, the extent of these effects depends on the difference between the means of the continuous outcome variable for the two levels of the predictor variable. An empirical example is given using data on education and blood pressure (dichotomized to create a high blood pressure us low blood pressure variable). Except at each end of the distribution, the results follow the hypothetical example. The observation has implications for public health and medical treatment; different cutpoints should be examined to determine the optimal cutpoint in terms of policy and/or treatment decisions. The observation described here also has implications for statistical interpretation; statements about the magnitude of association or statistical significance have limited meaning unless both the cutpoint and the distribution of the outcome variable are specified. (Epidemiology 1992;3:434–440)

Occupational disability due to low back pain: a new interdisciplinary classification based on a phase model of disability.

Study Design This study critically reviewed current conceptualizations of occupational disability resulting from low back pain (LBP). It proposes a new classification system for back pain built on a phase-model of disability. Objectives The goal was to develop a classification system that overcomes the shortcomings of existing classification schemes and is useful for interdisciplinary research, prevention, treatment, and rehabilitation. Summary of Background Data Attempts to study and prevent disability resulting from LBP have been hampered by the use of inadequate classifications of LBP. Methods Current classifications of LBP were critically reviewed, and criteria for a useful classification system are described. The disabling process is organized in eight consecutive phases determined by the presence and duration of work disability. Results The proposed eight-phase classification is based primarily on the presence and duration of work-disability rather than on clinical categories. It takes into account the developmental and social character of disability. The simplicity, reliability, and expandability of the model allow for its interdisciplinary use in research and intervention. Conclusion The prevention of disabling back pain requires an interdisciplinary approach. For this purpose, other than purely biomedical classifications of LBP are needed. The authors propose an eight-phase classification system primarily based on the duration of work disability and that takes into account other biomedical, developmental, and social characteristics of work-disability resulting from LBP.

Comorbidity and breast cancer survival: a comparison between black and white women.

The presence of concurrent health conditions (comorbidity) at the time of breast cancer diagnosis has an adverse effect on survival. It is unclear, however, whether the strength of the association between comorbidity and survival varies in different populations of breast cancer patients. It is necessary, therefore, to establish (1) whether a comorbidity index derived from a general population of patients (mostly white) would predict survival in a black population, and (2) whether comorbidity would have the same degree of relationship to mortality in black as in white populations. We studied 1196 breast cancer patients who were members of the Kaiser Permanente Medical Care Program and were diagnosed with local (n = 708), regional (n = 446), or remote (n = 49) stage breast cancer from 1973 to 1986. Mortality follow-up was completed to December 1994. Ten-year survival was studied in relation to the Charlson comorbidity index for black women and for white women, and for both groups of women combined. Compared to women with a Charlson comorbidity score of 0 (no comorbidity), patients with scores of 1, 2, and 3+ had risk ratios for ten-year mortality of 1.23 (P = 0.10), 2.58 (P < 0.001), and 3.44 (P < 0.001), respectively. This pattern of risk associated with comorbidity was similar to that found in the original Charlson study. The pattern of risk ratios for different levels of comorbidity was very similar for black and white patients. The results confirm previous studies indicating that comorbidity (in particular, the Charlson Comorbidity Index) predicts the survival of women with breast cancer, independently of other factors, such as stage of breast cancer at diagnosis. The Charlson index has prognostic significance for both black and white populations. Research is needed to determine whether the Charlson index can be improved by including health conditions that are particularly prevalent or severe in specific subgroups of women.

Objective stress factors, accidents, and absenteeism in transit operators : a theoretical framework and empirical evidence

The authors used observational job analysis as a conceptually based technique to measure stress factors unbiased by worker appraisal with 81 transit driving tasks on 27 transit lines. Stressor dimensions included work barriers that interfere with task performance due to poor technical-organizational design, time pressure, time binding (autonomy over time management), and monotonous conditions. Line-specific average stressor values were assigned to 308 transit operators who mainly worked the particular line. Logistic regression analyses showed associations for high work barriers and sickness absences (odds ratio [OR] = 3.8, p = .05). There were elevated risks for work accidents for high time pressure operators (OR = 4.0, p = .04) and for the medium time-binding group (OR = 3.3, p = .04) and significant (alpha = .20) unadjusted interaction terms for barriers and time pressure in predicting accidents and absences, and barriers and time binding in predicting absences. Findings suggest guaranteed rest breaks and flexible timing for accident prevention and removal of work barriers for reducing absenteeism.

Prevention of non-insulin-dependent diabetes mellitus with physical activity.

Physical activity has been recommended by physicians in managing patients with noninsulin-dependent diabetes mellitus (NIDDM); however, it is unclear whether physical activity can prevent this disease. Several prospective studies have suggested that increased physical activity may lead to the prevention of NIDDM. In the University of Pennsylvania Alumni Health Study, 5990 men were surveyed to determine the relationship between physical activity and the development of NIDDM. A total of 202 men developed NIDDM from 1962 to 1976. Leisure-time physical activity, expressed in kilocalories (kcal) was inversely related to the development of NIDDM. Incidence rates declined as energy expenditure increased. For each 2000-kcal increment in energy expenditure, the risk of NIDDM was reduced by 24% [relative risk (RR) 0.76, 95% confidence interval (CI) 0.63-0.92]. This association remained when adjusting for obesity, hypertension, and parental history of diabetes. The protective effect of physical activity was strongest in individuals at highest risk for NIDDM. Based on the review of data from several large prospective studies, it is quite likely that increased levels of physical activity are effective in preventing NIDDM, and the protective benefit is especially pronounced in those individuals who have the highest risk of disease.

Body mass index and 15-year mortality in a cohort of black men and women.

The association between body mass index (BMI) and mortality was investigated in 2453 black male (aged 30-79 years) and 2731 black female (aged 40-79 years) members of the Kaiser Foundation Health Plan. During a 15-year follow-up 393 male and 283 female deaths were identified. Analyses were conducted separately in a lower and an upper range of BMI (as well as over the entire range), to isolate separate effects of low weight and high weight on mortality. Particular attention was also paid to potential bias from cigarette smoking and antecedent illness. Cox regression analyses showed that over the entire range of BMI the adjusted BMI-mortality association was significantly J-shaped for the men and essentially flat for the women. The inverse association between BMI and mortality in the lower range of BMI was statistically significant for the men; the adjusted relative hazard increasing from the 10th to the 50th percentile of BMI was 0.76 (95% confidence interval [CI] 0.59-0.98). The positive association between BMI and mortality in the upper range of BMI was highly statistically significant for the men; the adjusted relative hazard increasing from the 50th to the 90th percentile of BMI was 1.37 (95% CI 1.14-1.63). Whether controlled by multivariate analysis, by excluding the first 5 years of follow-up from the analyses, or by analyzing the BMI-mortality association in smoking-specific and/or illness-specific subgroups, smoking and antecedent illness did not have much impact on the BMI-mortality association, in either sex. The general observations on the BMI-mortality association are similar to findings in some white cohorts.

Objective measurement of occupational stress factors--an example with San Francisco urban transit operators.

Eighty-one observational work analyses were conducted to measure stressors independently of worker appraisal in the San Francisco transit system. On the basis of action regulation theory, stress factors were defined as hindrances for task performance due to poor work organization or technological design. Stressors included (a) work barriers, defined as obstacles that cause extra work or unsafe behavior; (b) time pressure; (c) monotonous conditions; and (d) time binding, defined as control over timing. Reliability, measured as interrater agreement, ranged between 80 and 97%, with kappas of .46-.70. Validity analyses were done with 71 transit operators who participated in the observations and 177 operators who were assigned mean line-specific observational stressor measures. High odds ratios (ORs) were found for barriers and psychosomatic complaints (OR = 3.8, p = .00), time pressure and relaxation time needed after work (OR = 3.1, p = .05), and barriers and smoking to cope (OR = 3.8, p = .02). Using observational data in conjunction with self-report data can reduce confounding and improve interpretability of stress and health studies. Language: en

Physical Workload and Ergonomic Factors Associated With Prevalence of Back and Neck Pain in Urban Transit Operators

Study Design. Back and neck pain was studied crosssectionally in 1,449 urban transit drivers by linking medical data, self‐reported ergonomic factors, and company records on job history. Objectives. The goal was to examine the relation between physical workload, ergonomic factors, and the prevalence of back and neck pain. Summary of Background Data. Researchers, to date, have not found an independent effect of ergonomic factors on back and neck pain while accounting for the effects of past and current physical workload. Methods. Self‐reported ergonomic factors, vehicle type, physical workload (measured as duration of driving), height, weight, age, and gender were analyzed in relation to back and neck pain, using multivariable logistic regression models. Results. Physical workload showed a positive dose‐response relation with back and neck pain after controlling for vehicle type, height, weight, age, and gender. The odds ratio for 10 years of driving was 3.43. Additional adjustment for ergonomic factors decreased this odds ratio to 2.55. Six out of seven ergonomic factors were significantly related to the prevalence of back and neck pain after adjustment for age, gender, height, weight, and physical workload. Problems with adjusting the seat had the largest effect (odds ratio = 3.52). Women had back and neck pain twice as frequently as men. Conclusion. The results support the hypothesis of a causal role of physical workload for the development of back and neck pain. Ergonomic factors partially mediated the risk of back and neck pain associated with driving, suggesting a potential for prevention of back and neck pain by ergonomic redesign of transit vehicles. Elevated risks for back and neck pain for female drivers were not explained by anthropometric and ergonomic factors.