There are two common misconceptions about case-control studies: that matching in itself eliminates (controls) confounding by the matching factors, and that if matching has been performed, then a “matched analysis” is required. However, matching in a case-control study does not control for confounding by the matching factors; in fact it can introduce confounding by the matching factors even when...

Power calculations are derived for matched case-control studies in terms of the probability po of exposure among the control patients, the correlation coefficient phi for exposure between matched case and control patients, and the odds ratio psi for exposure in case and control patients. For given Type I and Type II error probabilities alpha and beta, the odds ratio that can be detected with a ...

Case-control studies occupy a central place in epidemiological research. The basic idea here is the comparison of a group (the “cases”) having the outcome of interest (normally some disease) with respect to a control group (those without disease) regarding one or more characteristics (exposure to certain external events). One of the early examples, which sparked a lot of debate in the fifties b...

Background. Mechanical relation between the foot and pelvic alignment had been studied in healthy subjects and individuals with other musculoskeletal disorders; however, in chronic ankle instability (CAI), it has not yet been determined. Objectives. To investigate the difference in pelvic torsion (PT) among individuals with CAI and uninjured subjects and correlate PT with perceived ankle insta...

Abstract. In this paper, we propose a uniaxial perfectly matched layer (PML) method for solving the time-harmonic scattering problems in two-layered media. The exterior region of the scatterer is divided into two half spaces by an infinite plane, on two sides of which the wave number takes different values. We surround the computational domain where the scattering field is interested by a PML l...