John J. Koval

The estimation of intraclass correlation in the analysis of family data.

The maximum likelihood estimator of the intraclass correlation coefficient rho in samples of unequal size from a multivariate normal distribution has been derived and compared to several other estimators, using Monte Carlo simulation. It is recommended that maximum likelihood be used if no prior knowledge concerning the value of rho is thought to be high. Fow low to moderate values of rho it is recommended that the analysis of variance estimator be used, with those families having only one member deleted from the analysis.

Does a relationship exist between body weight, concerns about weight, and smoking among adolescents? An integration of the literature with an emphasis on gender.

It has been speculated that body weight and concern about body weight are important factors in initiation of tobacco use among adolescents, particularly females. An examination of studies that have explored these relationships can provide important information on possible underlying mechanisms that could be used for prevention interventions. This review summarizes recent studies examining weight concerns and youth smoking, with a focus on gender differences. These studies were integrated with the few studies that have examined the relationship between actual body weight and smoking among adolescents. A total of 55 primary research articles met inclusion criteria for the review. Of these, 19 studies assessed the relationship between body weight and smoking, and 50 studies addressed weight concerns and smoking. Some evidence indicated a positive relationship between smoking and body weight among adolescents, although not all studies found a positive association. In terms of the relationship between weight concerns and adolescent smoking, the amount of evidence supporting a positive association differed depending on the dimension of weight concern considered, with the strongest evidence for dieting behaviors. For dieting behaviors, disordered eating symptoms, and some aspects of general weight concerns, the positive relationship with smoking was more consistent among female adolescents than among male adolescents. Possible explanations for these findings are discussed, and priorities for future research are identified.

Can primary care doctors prescribe exercise to improve fitness?: The step test exercise prescription (STEP) project

BACKGROUND Sedentary lifestyle is associated with adverse health outcomes. Available evidence suggests that, despite positive attitudes toward regular exercise in promoting a healthy lifestyle, few physicians actually prescribe exercise for their patients. Barriers include lack of skills and standard office instruments. Because primary care physicians have regular contact with a large proportion of the population, the impact of preventive health interventions may be great. OBJECTIVES To determine the effect of an exercise prescription instrument (i.e., Step Test Exercise Prescription [STEP]), compared to usual-care exercise counseling delivered by primary care doctors on fitness and exercise self-efficacy among elderly community-dwelling patients. DESIGN Randomized controlled trial; baseline assessment and intervention delivery with postintervention follow-up at 3, 6, and 12 months. SETTING Four large (>5000 active patient files) academic, primary care practices: three in urban settings and one in a rural setting, each with four primary care physicians; two clinics provided the STEP intervention and two provided usual care control. PARTICIPANTS A total of 284 healthy community-dwelling patients (72 per clinic) aged >65 years were recruited in 1998-1999. INTERVENTION STEP included exercise counseling and prescription of an exercise training heart rate. MAIN OUTCOME MEASURES The primary outcome measure was aerobic fitness (VO(2max)). Secondary outcomes included predicted VO(2max) from the STEP test, exercise self-efficacy (ESE), and clinical anthropometric parameters. RESULTS A total of 241 subjects (131 intervention, 110 control) completed the trial. VO(2max) was significantly increased in the STEP intervention group (11%; 21.3 to 24ml/kg/min) compared to the control group (4%; 22 to 23ml/kg/min) over 6 months (p <0.001), and 14% (21.3 to 24.9ml/kg/min) and 3% (22.1 to 22.8ml/kg/min), respectively, at 12 months (p <0.001). A similar significant increase in ESE (32%; 4.6 vs 6.8) was observed for the STEP group compared to the control group (22%; 4.2 vs 5.4) at 12 months (p < 0.001). Systolic blood pressure decreased 7.3% and body mass index decreased 7.4% in the STEP group, with no significant change in the control group (p <0.05). Exercise counseling time was significantly (p <0.02) longer in the STEP (11.7+/-3.0 min) compared to the control group (7.1+/-7.0 min), but more (p <0.05) subjects completed > or =80% of available exercise opportunities in the STEP group. CONCLUSIONS Primary care physicians can improve fitness and exercise confidence of their elderly patients using a tailored exercise prescription (e.g., STEP). Further, STEP appears to maintain benefits to 12 months and may improve exercise adherence. Future study should determine the impact of combining cognitive/behavior change strategies with STEP.

Longitudinal study of determinants of dependence in an elderly population.

Objectives: To describe those factors, from the host of initial measures in ambulatory, independent older men and women, that were determinants of becoming dependent over an 8‐year follow‐up.

Interval estimation for Cohen's kappa as a measure of agreement

Cohens kappa statistic is a very well known measure of agreement between two raters with respect to a dichotomous outcome. Several expressions for its asymptotic variance have been derived and the normal approximation to its distribution has been used to construct confidence intervals. However, information on the accuracy of these normal-approximation confidence intervals is not comprehensive. Under the common correlation model for dichotomous data, we evaluate 95 per cent lower confidence bounds constructed using four asymptotic variance expressions. Exact computation, rather than simulation is employed. Specific conditions under which the use of asymptotic variance formulae is reasonable are determined.

Stress-coping and other psychosocial risk factors : A model for smoking in grade 6 students

Smoking uptake by adolescents is best studied by a following a cohort of children as they proceed through adolescence. In this analysis of the first stage of such a study, several hypotheses about psychosocial factors that may modify the initiation of smoking in adolescents were examined in 1,552 11- and 12-year-olds in a school system in Scarborough, Canada. Investigation of the stress-coping hypothesis and other possible effect modifiers as they relate to ever-smoking revealed that stress (measured by number of life events) was important for both males and females (p = .0163 and .0056, respectively). However, the mechanisms underlying smoking appear to be different for males and females, even at this young age. In models adjusting for several factors simultaneously, rebelliousness was found to be the most important factor (p = .0001) followed by attitudes toward the effect of second-hand smoke (p = .0063) for males, whereas for females, mother smoking was the most important factor (p = .0001) followed by rebelliousness (p = .0102). Implications for design of prevention programs are discussed.

Are psychosocial factors related to smoking in grade-6 students ?

The associations of psychosocial characteristics with both gender and smoking behavior were explored in a sample of 1552 grade-six students from 107 schools in one Ontario, Canada, school district. Ever smokers were more likely to have spending money: a part-time job; to have missed school in previous 2 months; perceive themselves to be below average or average in school; to have a mother, a father, and a sibling who smoke; to have consumed low alcohol and alcoholic beverages; and agree with fewer positive statements concerning second-hand smoke and the addictive properties of smoking. Ever smokers had more close friends who tried smoking, spent more time with friends, scored higher on depression, rebelliousness, and social conformity scales, reported more life events in the past year, and had lower scores for social support. More boys than girls had ever smoked (18.9% vs. 14.7%). Gender differences were found for sociodemographic, attitudes, social bonding, and psychosocial factors.

A self-paced step test to predict aerobic fitness in older adults in the primary care clinic

OBJECTIVES: To study the potential usefulness of a submaximal self‐paced step test as a prediction of maximal aerobic capacity (VO2max) in older adults in the primary care setting.

Determination of the best significance level in forward stepwise logistic regression

The χ2 test based on a fixed a level (χ2 (a)) is the standard stopping criterion in forward stepwise logistic regression. SAS/IML programs were written to provide Monte Carlo simulations to determine the best a level for the χ2 (a) stopping criterion. Performance was evaluated using Efrons (1986) estimated true error rate of prediction. The best a varied between 0.05 and 0,40. In all cases, it increased linearly the number of predictor variables; in the multivariate binary case, it also depended upon the mean of the binary variables in one population and the difference between the means of the binary variables in the two populations. An overall recommendation is that 0.15 ≤ a ≤ 0.20 should be used for the χ2 (a) stopping criterion.

Comprehensive tobacco control policies and the smoking behaviour of Canadian adults

OBJECTIVE To examine the associations of cigarette prices, restrictions on public smoking, and health education with the odds of adult smoking and amount smoked daily. DESIGN Multi-level analysis of adult (age 25+) smoking patterns in Canadas National Population Health Survey, after adding administrative data on prices, bylaws, and health education according to the survey respondents place of residence. SETTING/SUBJECTS Population based sample of Canadians age 25+ in households (n = 14 355). OUTCOME MEASURES Smoking status, amount consumed daily. ANALYSIS Logistic regression for smoking status, multiple regression for amount smoked, with controls for age, education, marital status; separate analyses for men and women. RESULTS Cigarette prices were positively associated with the odds of being a non-smoker and negatively with amount smoked, for adults of both sexes. Per capita health education expenditures were positively associated with the odds of being a non-smoker and negatively with amount smoked—formen but not women. The restrictiveness of municipal bylaws limiting public smoking was positively associated with the odds of being a non-smoker and negatively with amount smoked—forwomen but not men. These results are independent of age, education, and marital status. CONCLUSIONS To be effective, tobacco control must comprise a mix of strategies as men and women respond differently to health education and restrictions on public smoking; taxation, reflected in higher cigarette prices, is the only one of these measures related to smoking for both sexes. This model permits calculations of the level of increase in each measure that is required to reduce the prevalence of smoking by a specified amount.