Trials in which intact communities are the units of randomization are increasingly being used to evaluate interventions which are more naturally administered at the community level, or when there is a substantial risk of treatment contamination. In this article we focus on the planning of community intervention trials in which k communities (for example, medical practices, worksites, or villages) are to be randomly allocated to each of an intervention and a control group, and fixed cohorts of m individuals enrolled in each community prior to randomization. Formulas to determine k or m may be obtained by adjusting standard sample size formulas to account for the intracluster correlation coefficient rho. In the presence of individual-level attrition however, observed cohort sizes are likely to vary. We show that conventional approaches of accounting for potential attrition, such as dividing standard sample size formulas by the anticipated follow-up rate pi or using the average anticipated cohort size m pi, may, respectively, overestimate or underestimate the required sample size when cluster follow-up rates are highly variable, and m or rho are large. We present new sample size estimation formulas for the comparison of two means or two proportions, which appropriately account for variation among cluster follow-up rates. These formulas are derived by specifying a model for the binary missingness indicators under the population-averaged approach, assuming an exchangeable intracluster correlation coefficient, denoted by tau. To aid in the planning of future trials, we recommend that estimates for tau be reported in published community intervention trials.
Shorter stature is an established risk factor for coronary artery disease (CAD), but less is known about its association with extent of the disease.
We assessed the relationship between self-reported height and angiographic findings in 7706 men and 3572 women identified from a nationwide coronary angiography registry in Iceland.
After adjustment for traditional cardiovascular risk factors, a standard deviation decrease in height associated with a greater likelihood of significant CAD (defined as =50% luminal diameter stenosis) both in men (adjusted odds ratio [ORadj]: 1.24, 95% confidence interval [CI]: 1.18, 1.31; p = 3.2 × 10-16) and women (ORadj = 1.10, 95% CI: 1.02, 1.18; p = 0.012). In partial proportional odds logistic regression models, a standard deviation decrease in height was associated with higher odds of having greater extent of CAD in men (ORadj = 1.19, 95% CI: 1.15, 1.25; p = 1.5 × 10-16) and women (ORadj = 1.09, 95% CI: 1.02, 1.16; p = 0.014). When limited to patients with significant CAD, the association was statistically significant in men (ORadj = 1.08, 95% CI: 1.03, 1.14; p = 0.0022) but not in women (p = 0.56).
Our findings show that shorter stature is associated with greater extent of coronary atherosclerosis in a large unselected population of individuals undergoing coronary angiography. This relationship appears to be sex-dependent, with stronger effects in men than in women.
Cardiac arrest is the leading cause of mortality in Canada, and the overall survival rate for out-of-hospital cardiac arrest rarely exceeds 5%. Bystander cardiopulmonary resuscitation (CPR) has been shown to increase survival for cardiac arrest victims. However, bystander CPR rates remain low in Canada, rarely exceeding 15%, despite various attempts to improve them. Dispatch-assisted CPR instructions have the potential to improve rates of bystander CPR and many Canadian urban communities now offer instructions to callers reporting a victim in cardiac arrest. Dispatch-assisted CPR instructions are recommended by the International Guidelines on Emergency Cardiovascular Care, but their ability to improve cardiac arrest survival remains unclear.
The overall goal of this study is to better understand the factors leading to successful dispatch-assisted CPR instructions and to ultimately save the lives of more cardiac arrest patients. The study will utilize a before-after, prospective cohort design to specifically: 1) Determine the ability of 9-1-1 dispatchers to correctly diagnose cardiac arrest; 2) Quantify the frequency and impact of perceived agonal breathing on cardiac arrest diagnosis; 3) Measure the frequency with which dispatch-assisted CPR instructions can be successfully completed; and 4) Measure the impact of dispatch-assisted CPR instructions on bystander CPR and survival rates.The study will be conducted in 19 urban communities in Ontario, Canada. All 9-1-1 calls occurring in the study communities reporting out-of-hospital cardiac arrest in victims 16 years of age or older for which resuscitation was attempted will be eligible. Information will be obtained from 9-1-1 call recordings, paramedic patient care reports, base hospital records, fire medical records and hospital medical records. Victim, caller and system characteristics will be measured in the study communities before the introduction of dispatch-assisted CPR instructions (before group), during the introduction (run-in phase), and following the introduction (after group).
The study will obtain information essential to the development of clinical trials that will test a variety of educational approaches and delivery methods for telephone cardiopulmonary resuscitation instructions. This will be the first study in the world to clearly quantify the impact of dispatch-assisted CPR instructions on survival to hospital discharge for out-of-hospital cardiac arrest victims.
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Low participation in population-based follow-up studies addressing psychosocial risk factors may cause biased estimation of health risk but the issue has seldom been examined. We compared risk estimates for selected health outcomes among respondents and the entire source population.
In a Danish cohort study of associations between psychosocial characteristics of the work environment and mental health, the source population of public service workers comprised 10,036 employees in 502 work units of which 4,489 participated (participation rate 45%). Data on the psychosocial work environment were obtained for each work unit by calculating the average of the employee self-reports. The average values were assigned all employees and non-respondent at the work unit. Outcome data on sick leave and prescription of antidepressant medication during the follow-up period (1.4.2007-31.12.2008) was obtained by linkage to national registries.
Respondents differed at baseline from non-respondents by gender, age, employment status, sick leave and hospitalization for affective disorders. However, risk estimates for sick leave and prescription of antidepressant medication, during follow-up, based on the subset of participants, did only differ marginally from risk estimates based upon the entire population.
We found no indications that low participation at baseline distorts the estimates of associations between the work unit level of psychosocial work environment and mental health outcomes during follow-up. These results may not be valid for other exposures or outcomes.
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BACKGROUND: Studies evaluating safety of different birth settings for low-risk deliveries are often difficult to interpret because of great methodological problems. OBJECTIVE: To assess potential bias in comparisons of mortality between maternity institutions with different size and level of care, particularly when using various definitions of low-risk delivery and when studying stillbirth rates. DESIGN: Population-based study. POPULATION: The population of 1.74 million births in Norway from 1967 to 1996 recorded in The Medical Birth Registry of Norway. METHODS: First we explored the problems of properly identifying low-risk deliveries from population-based data and calculated adjusted perinatal mortality rates in sub-populations by excluding different risk factors. Then we measured the difference in apparent low-risk deliveries between institutions of different size and level of care. Finally we explored bias by using stillbirths and discuss the loss of statistical power by studying only livebirths. RESULTS: The occurrence of a whole spectrum of risk factors differed between small and large institutions, even after adjustment for birthweight. Although the majority of births were from low-risk deliveries, only 1/10th of all perinatal deaths occurred in this group after admission to a maternity unit. There was a systematic difference in the reporting of time of death for stillbirths between types of institutions; the rate of stillbirths occurring during delivery was higher among small institutions, while large institutions were more often uncertain in classifying time of death for stillbirths. CONCLUSIONS: Adjustments for a large number of different risk factors, large sample-sizes and caution in including stillbirth as outcome measure are needed when comparisons of safety between different sizes of delivery units are made for low-risk pregnancies.
The study addresses the characteristics potentially predictive of non-response to a health survey among 2500 24-year-old males, on whom a notable amount of other data was available. The overall non-response rate was 40%, part of which was due to the unreachability of some subjects: 4% of the questionnaires were returned because of unknown addresses. Some (n = 39) of the respondents had concealed the identification number in the questionnaire, which made it impossible to link these data to those collected before in their cases. We were therefore able to use effectively the data on 1450 (58%) responding subjects in this paper. Failure to respond was more common among the subjects who had lived in towns in their youth, had not grown up in a complete family, whose socioeconomic status of the family was unknown, and whose mother was young and had a low educational level. Poorer-than-average school performance at elementary school was also predictive of a high non-response rate. Non-response was heavily associated with previous non-response to a health inquiry. Some aspects of health and behaviour in adolescense, such as smoking at the age of 14, were related to non-response to this survey, too. The non-response was higher than average among those subjects who had suffered from mental disorders (serious mental disorders, less serious mental disorders such as neurotic disorders, adjustment reactions, and psychosomatic disorders and mental retardation). The young men who were employed, were students or were doing military service at the age 24 responded better than those who were unemployed or at disability pension.
The clinical pathway is a tool that operationalizes best evidence recommendations and clinical practice guidelines in an accessible format for 'point of care' management by multidisciplinary health teams in hospital settings. While high-quality, expert-developed clinical pathways have many potential benefits, their impact has been limited by variable implementation strategies and suboptimal research designs. Best strategies for implementing pathways into hospital settings remain unknown. This study will seek to develop and comprehensively evaluate best strategies for effective local implementation of externally developed expert clinical pathways.
We will develop a theory-based and knowledge user-informed intervention strategy to implement two pediatric clinical pathways: asthma and gastroenteritis. Using a balanced incomplete block design, we will randomize 16 community emergency departments to receive the intervention for one clinical pathway and serve as control for the alternate clinical pathway, thus conducting two cluster randomized controlled trials to evaluate this implementation intervention. A minimization procedure will be used to randomize sites. Intervention sites will receive a tailored strategy to support full clinical pathway implementation. We will evaluate implementation strategy effectiveness through measurement of relevant process and clinical outcomes. The primary process outcome will be the presence of an appropriately completed clinical pathway on the chart for relevant patients. Primary clinical outcomes for each clinical pathway include the following: Asthma--the proportion of asthmatic patients treated appropriately with corticosteroids in the emergency department and at discharge; and Gastroenteritis--the proportion of relevant patients appropriately treated with oral rehydration therapy. Data sources include chart audits, administrative databases, environmental scans, and qualitative interviews. We will also conduct an overall process evaluation to assess the implementation strategy and an economic analysis to evaluate implementation costs and benefits.
This study will contribute to the body of evidence supporting effective strategies for clinical pathway implementation, and ultimately reducing the research to practice gaps by operationalizing best evidence care recommendations through effective use of clinical pathways.