which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Yan et al. have published a useful paper about thyroid dysfunction (TD) in cases with hepatitis C by treatment with interferon (1). There are some comments which may explicit benefits of this paper in more details. When we report a methodological or statistical issue it is...

background  & aim: case-crossover  studies are the case-control  version of crossover studies. in these studies, cases and controls are the same subjects. the term crossover is applied for designs that all subjects pass through both treatment (exposure) and placebo (non-exposure) phases. in fact they are  crossover  of  subjects  between  periods  of  exposure  and  non-exposure.  this  design ...