Calculation of NNTs in RCTs with time-to-event outcomes: A literature review

Abstract Background The number needed to treat (NNT) is a well-known effect measure for reporting the results of clinical trials. In the case of time-to-event outcomes, the calculation of NNTs is more difficult than in the case of binary data. The frequency of using NNTs to report results of randomised controlled trials (RCT) investigating time-to-event outcomes and the adequacy of the applied calculation methods are unknown. Methods We searched in PubMed for RCTs with parallel group design and individual randomisation, published in four frequently cited journals between 2003 and 2005. We evaluated the type of outcome, the frequency of reporting NNTs with corresponding confidence intervals,…

Euclid preparation. XII. Optimizing the photometric sample of the Euclid survey for galaxy clustering and galaxy-galaxy lensing analyses

Pocino, A., et al. (Euclid Collaboration)

Generating survival times to simulate Cox proportional hazards models

Simulation studies present an important statistical tool to investigate the performance, properties and adequacy of statistical models in pre-specified situations. One of the most important statistical models in medical research is the proportional hazards model of Cox. In this paper, techniques to generate survival times for simulation studies regarding Cox proportional hazards models are presented. A general formula describing the relation between the hazard and the corresponding survival time of the Cox model is derived, which is useful in simulation studies. It is shown how the exponential, the Weibull and the Gompertz distribution can be applied to generate appropriate survival times f…

Euclid preparation: XI. Mean redshift determination from galaxy redshift probabilities for cosmic shear tomography

Ilbert, O., et al. (Euclid Collaboration)

Calculating confidence intervals for impact numbers

Abstract Background Standard effect measures such as risk difference and attributable risk are frequently used in epidemiological studies and public health research to describe the effect of exposures. Recently, so-called impact numbers have been proposed, which express the population impact of exposures in form of specific person or case numbers. To describe estimation uncertainty, it is necessary to calculate confidence intervals for these new effect measures. In this paper, we present methods to calculate confidence intervals for the new impact numbers in the situation of cohort studies. Methods Beside the exposure impact number (EIN), which is equivalent to the well-known number needed …

S41.1: A general approach to generate survival times in simulation studies

Estimating adjusted NNT measures in logistic regression analysis

The number needed to treat (NNT) is a popular measure to describe the absolute effect of a new treatment compared with a standard treatment or placebo in clinical trials with binary outcome. For use of NNT measures in epidemiology to compare exposed and unexposed subjects, the terms 'number needed to be exposed' (NNE) and 'exposure impact number' (EIN) have been proposed. Additionally, in the framework of logistic regression a method was derived to perform point and interval estimation of NNT measures with adjustment for confounding by using the adjusted odds ratio (OR approach). In this paper, a new method is proposed which is based upon the average risk difference over the observed confou…

Predictors of Adherence to the Use of Hip Protectors in Nursing Home Residents

Objectives: To assess predictors of hip-protector use in nursing home residents under usual-care conditions and after intervention consisting of structured education of nurses and nursing home residents and provision of free hip protectors. Design: Nested cohort analyses within a cluster randomized, controlled trial with 18 months follow-up. Setting: Forty-nine nursing home clusters in Hamburg, Germany. Participants: Residents with at least one fall during the study period (intervention group, n=237; usual-care group, n=274). Measurements: Use of hip protector while falling. Regression analyses were performed for each of the two cohorts of fallers using the time to the first fall without hi…

Generating survival times to simulate Cox proportional hazards models by Ralf Bender, Thomas Augustin and Maria Blettner,Statistics in Medicine 2005;24:1713–1723

Eight-year trends in food, energy and macronutrient intake in a sample of elderly German subjects.

Time trends in the food and the corresponding energy and macronutrient intake between 1994 and 2002 are investigated as part of the longitudinal study on nutrition and health status in an ageing population in Giessen, Germany (GISELA study). The dietary intake is assessed via a 3 d estimated dietary record especially developed and validated for this study. A total of 2135 records from 532 subjects, aged 60 years and over, are analysed separately according to sex and age groups (born 1904–1928 and born 1929–1942). Results show that the food, energy and macronutrient intake of the GISELA subjects stayed fairly stable over the study period. However, some significant changes in the consumption …

Euclid Preparation. XIV. The Complete Calibration of the Color–Redshift Relation (C3R2) Survey: Data Release 3

Stanford, S. A., et al.