Crude incidence in two-phase designs in the presence of competing risks.

BackgroundIn many studies, some information might not be available for the whole cohort, some covariates, or even the outcome, might be ascertained in selected subsamples. These studies are part of a broad category termed two-phase studies. Common examples include the nested case-control and the case-cohort designs. For two-phase studies, appropriate weighted survival estimates have been derived; however, no estimator of cumulative incidence accounting for competing events has been proposed. This is relevant in the presence of multiple types of events, where estimation of event type specific quantities are needed for evaluating outcome.MethodsWe develop a non parametric estimator of the cumulative incidence function of events accounting for possible competing events. It handles a general sampling design by weights derived from the sampling probabilities. The variance is derived from the influence function of the subdistribution hazard.ResultsThe proposed method shows good performance in simulations. It is applied to estimate the crude incidence of relapse in childhood acute lymphoblastic leukemia in groups defined by a genotype not available for everyone in a cohort of nearly 2000 patients, where death due to toxicity acted as a competing event. In a second example the aim was to estimate engagement in care of a cohort of HIV patients in resource limited setting, where for some patients the outcome itself was missing due to lost to follow-up. A sampling based approach was used to identify outcome in a subsample of lost patients and to obtain a valid estimate of connection to care.ConclusionsA valid estimator for cumulative incidence of events accounting for competing risks under a general sampling design from an infinite target population is derived

Is there a demand for physical activity interventions provided by the health care sector? Findings from a population survey

<p>Abstract</p> <p>Background</p> <p>Health care providers in many countries have delivered interventions to improve physical activity levels among their patients. Thus far, less is known about the population's interest to increase their physical activity levels and their opinion about the health care provider's role in physical activity promotion. The aims of this paper were to investigate the self-reported physical activity levels of the population and intention to increase physical activity levels, self-perceived need for support, and opinions about the responsibilities of both individuals and health care providers to promote physical activity.</p> <p>Methods</p> <p>A regional public health survey was mailed to 13 440 adults (aged 18-84 years) living in Östergötland County (Sweden) in 2006. The survey was part of the regular effort by the regional Health Authorities.</p> <p>Results</p> <p>About 25% of the population was categorised as physically active, 38% as moderately active, 27% as somewhat active, and 11% as low active. More than one-third (37%) had no intentions to increase their physical activity levels, 36% had thought about change, while 27% were determined to change. Lower intention to change was mainly associated with increased age and lower education levels. 28% answered that physical activity was the most important health-related behaviour to change "right now" and 15% of those answered that they wanted or needed support to make this change. Of respondents who might be assumed to be in greatest need of increased activity (i.e. respondents reporting poor general health, BMI>30, and inactivity) more than one-quarter wanted support to make improvements to their health. About half of the respondents who wanted support to increase their physical activity levels listed health care providers as a primary source for support.</p> <p>Conclusions</p> <p>These findings suggest that there is considerable need for physical activity interventions in this population. Adults feel great responsibility for their own physical activity levels, but also attribute responsibility for promoting increased physical activity to health care practitioners.</p

Reaching the Hard-to-Reach: A Probability Sampling Method for Assessing Prevalence of Driving under the Influence after Drinking in Alcohol Outlets

Drinking alcoholic beverages in places such as bars and clubs may be associated with harmful consequences such as violence and impaired driving. However, methods for obtaining probabilistic samples of drivers who drink at these places remain a challenge – since there is no a priori information on this mobile population – and must be continually improved. This paper describes the procedures adopted in the selection of a population-based sample of drivers who drank at alcohol selling outlets in Porto Alegre, Brazil, which we used to estimate the prevalence of intention to drive under the influence of alcohol. The sampling strategy comprises a stratified three-stage cluster sampling: 1) census enumeration areas (CEA) were stratified by alcohol outlets (AO) density and sampled with probability proportional to the number of AOs in each CEA; 2) combinations of outlets and shifts (COS) were stratified by prevalence of alcohol-related traffic crashes and sampled with probability proportional to their squared duration in hours; and, 3) drivers who drank at the selected COS were stratified by their intention to drive and sampled using inverse sampling. Sample weights were calibrated using a post-stratification estimator. 3,118 individuals were approached and 683 drivers interviewed, leading to an estimate that 56.3% (SE = 3,5%) of the drivers intended to drive after drinking in less than one hour after the interview. Prevalence was also estimated by sex and broad age groups. The combined use of stratification and inverse sampling enabled a good trade-off between resource and time allocation, while preserving the ability to generalize the findings. The current strategy can be viewed as a step forward in the efforts to improve surveys and estimation for hard-to-reach, mobile populations