213 research outputs found
Second-harmonic generation with zero group-velocity mismatch in nonlinear photonic crystal fibers
Estimating a population cumulative incidence under calendar time trends
Abstract
Background
The risk of a disease or psychiatric disorder is frequently measured by the age-specific cumulative incidence. Cumulative incidence estimates are often derived in cohort studies with individuals recruited over calendar time and with the end of follow-up governed by a specific date. It is common practice to apply the Kaplan\u2013Meier or Aalen\u2013Johansen estimator to the total sample and report either the estimated cumulative incidence curve or just a single point on the curve as a description of the disease risk.
Methods
We argue that, whenever the disease or disorder of interest is influenced by calendar time trends, the total sample Kaplan\u2013Meier and Aalen\u2013Johansen estimators do not provide useful estimates of the general risk in the target population. We present some alternatives to this type of analysis.
Results
We show how a proportional hazards model may be used to extrapolate disease risk estimates if proportionality is a reasonable assumption. If not reasonable, we instead advocate that a more useful description of the disease risk lies in the age-specific cumulative incidence curves across strata given by time of entry or perhaps just the end of follow-up estimates across all strata. Finally, we argue that a weighted average of these end of follow-up estimates may be a useful summary measure of the disease risk within the study period.
Conclusions
Time trends in a disease risk will render total sample estimators less useful in observational studies with staggered entry and administrative censoring. An analysis based on proportional hazards or a stratified analysis may be better alternatives
Understanding the neurocognitive organization as strategies rather than functions: Implications for neurological research
Free diving-inspired breathing techniques for COPD patients:A pilot study
Objectives: Pulmonary rehabilitation (PR) is a key factor in enhancing self-management and exercise capacity in patients with chronic obstructive pulmonary disease (COPD). The content and length of PR varies between countries and authorities responsible for rehabilitation. After completion of rehabilitation, it is often difficult for patients to stay motivated and perform regular exercise. Methods: In this pilot study, nine patients with moderate to severe COPD completed a 6-week training programme consisting of free diving-inspired breathing techniques, designed to be incorporated into daily activities. Results: Participants significantly increased the distance walked in 6Â min by 48Â m (p < 0.05) and a significant reduction was seen on the COPD self-efficacy scale (p < 0.05). Furthermore, adherence to the programme sessions was very high at 96.3% and no adverse events occurred. Discussion: This pilot study tested the feasibility of introducing breathing techniques used by COPD patients to enhance their walking capacity. The techniques were well tolerated and participantâs adherence to the weekly group sessions was high
Freestanding midwifery unit versus obstetric unit: a matched cohort study of outcomes in low-risk women
- âŚ