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Melvyn Hillsdon

Publications and source records attributed to Melvyn Hillsdon.

6 recordsLinked to original sources
PubMed2004

Comparison of imputation and modelling methods in the analysis of a physical activity trial with missing outcomes.

BACKGROUND: Longitudinal studies almost always have some individuals with missing outcomes. Inappropriate handling of the missing data in the analysis can result in misleading conclusions. Here we review a wide range of methods to handle missing outcomes in single and repeated measures data and discuss which methods are most appropriate. METHODS: Using data from a randomized controlled trial to compare two interventions for increasing physical activity, we compare complete-case analysis; ad hoc imputation techniques such as last observation carried forward and worst-case; model-based imputation; longitudinal models with random effects; and recently proposed joint models for repeated measures data and non-ignorable dropout. RESULTS: Estimated intervention effects from ad hoc imputation methods vary widely. Standard multiple imputation and longitudinal modelling agree closely, as they should. Modifying the modelling method to allow for non-ignorable dropout had little effect on estimated intervention effects, but imputing using a common imputation model in both groups gave more conservative results. CONCLUSIONS: Results from ad hoc imputation methods should be avoided in favour of methods with more plausible assumptions although they may be computationally more complex. Although standard multiple imputation methods and longitudinal modelling methods are equivalent for estimating the treatment effect, the two approaches suggest different ways of relaxing the assumptions, and the choice between them depends on contextual knowledge.

Bias↗
PubMed2004

Can a simple measure of vigorous physical activity predict future mortality? Results from the OXCHECK study.

BACKGROUND: As epidemiological studies have become more complex, demands for short, easily administered measures of risk factors have increased. This study investigates whether such a measure of physical activity is associated with the risk of death from all causes and death from specific causes. METHODS: A prospective follow-up study of 11,090 men and women, aged 35-64 years, recruited from five UK general practices who responded to a postal questionnaire in 1989. Self-reported frequency of vigorous-intensity physical activity and data on confounding factors were collected at baseline survey. Death notifications up to 31 December 2001 were provided by the Office for National Statistics. The relative risk (and 95% confidence interval) of dying associated with each level of exposure to physical activity was estimated by the hazard ratio in a series of Cox regression models. RESULTS: After >10 years' follow-up there were 825 deaths among the 10 522 subjects with no previous history of angina or myocardial infarction. Participation in vigorous exercise was associated with a significantly lower risk of all-cause mortality. Similar associations were found for ischaemic heart disease and cancer mortality, although the relationships were not significant at the 5% level. CONCLUSIONS: Simple measures of self-reported vigorous physical activity are associated with the risk of future mortality, at least all-cause mortality in a somewhat selected group. Interpretation of the finding should be treated with caution due to the reliance on self-report and the possibility that residual confounding may underlie the associations. Because moderate-intensity physical activity is also beneficial to health, short physical activity questionnaires should include measures of such physical activity in the future.

Adult↗
PubMed2004

Changing the environment to promote health-enhancing physical activity.

Supportive environments have been used to change and influence health behaviours like smoking. While psychological and ecological theories and models demonstrate the possible influences of the environment on health-enhancing physical activity (HEPA), little is known about the effectiveness of the environmental interventions. This paper presents the results of a systematic review of studies that used environmental interventions to increase health-enhancing physical activity. Two groups of studies were found, studies that changed the physical environment by creating new HEPA facilities, policies and supporting mechanisms, and studies that used the elements of the environment as an active or sedentary 'point of choice', via educational materials to promote stair use. Environmental change studies showed a small increase on HEPA behaviour, but the relative impact of environment changes was not evaluated. A number of before and after studies have observed a weak effect of a simple environmental change to stimulate stair climbing while travelling or shopping. Current national policy has embraced the environment as an option for promoting health-enhancing physical activity, especially active travel, in spite of the lack of effectiveness data. It is recommended that existing or planned public health environment and HEPA initiatives should use appropriate evaluation methods to assess their efficacy and effectiveness. Further developmental research into the nature of the relationship of the environment to particular HEPA behaviours is strongly recommended before developing new environmental interventions.

Environment Design↗
PubMed2002

Advising people to take more exercise is ineffective: a randomized controlled trial of physical activity promotion in primary care.

BACKGROUND: Over the last 10 years 'exercise referral schemes' have been popular even though the evidence for effectiveness of any one-to-one intervention in primary care is deficient. We report the results of a primary care based one-to-one intervention that compared the effect of two communication styles with a no-intervention control group on self-reported physical activity at 12 months. METHODS: In all, 1658 middle-aged men and women were randomly assigned to 30 minutes of brief negotiation or direct advice in primary care or a no-intervention control group. The main outcome was self-reported physical activity at 12 months. Secondary outcome measures included change in blood pressure and body mass index. RESULTS: Intention-to-treat analysis revealed no significant differences in physical activity between groups. Brief negotiation group participants who completed the study increased their physical activity significantly more than controls. There was no change in body mass index in any group. The brief negotiation group produced a greater reduction in diastolic blood pressure than direct advice. CONCLUSION: If patients whose health may benefit from increased physical activity seek advice in primary care, 20-30 minutes of brief negotiation to increase physical activity is probably more effective than similar attempts to persuade or coerce. However, blanket physical activity promotion in primary care is not effective. The most effective way of increasing physical activity in primary care has yet to be determined.

Energy Metabolism↗