background hepatitis b virus (hbv) is one of the most common chronic viral infections in the world. iran has a low to intermediate hbv prevalence and approximately 1.5 million people are living with hbv infection. the impact of hbv in iran is unknown and given the very low levels of alcohol consumption, this region provides an opportunity to examine the impact of isolated chronic hbv infection....

Received 22 November 2004 _________________________ C onfounding is a major concern in causal studies because it results in biased estimation of exposure effects. In the extreme, this can mean that a causal effect is suggested where none exists, or that a true effect is hidden. Typically, confounding occurs when there are differences between the exposed and unexposed groups in respect of indepe...

According to the authors, time-modified confounding occurs when the causal relation between a time-fixed or time-varying confounder and the treatment or outcome changes over time. A key difference between previously described time-varying confounding and the proposed time-modified confounding is that, in the former, the values of the confounding variable change over time while, in the latter, t...