It has long been hypothesized that exposure to television is a risk factor for aggression and violence; the earliest public hearings on the question took place in 1952, when fewer than one quarter of US households possessed television sets (1). Over the years, there have been scores of research reports on the issue (2-4), as well as several major governmental investigations (5-7). Throughout th...

Studies in the field of ‘molecular epidemiology’ are becoming common in the literature. This use of molecular-biological laboratory techniques in epidemiological research has some consequences that deserve specific attention, including the potential for some particular forms of bias. Most of the bias in epidemiological research, at large, occurs because of imperfect sampling or classification p...

Triangulation is the practice of obtaining more reliable answers to research questions through integrating results from several different approaches, where each approach has different key sources of potential bias that are unrelated to each other. With respect to causal questions in aetiological epidemiology, if the results of different approaches all point to the same conclusion, this strength...

The internal validity of an epidemiological study can be affected by random error and systematic error. Random error reflects a problem of precision in assessing a given exposure-disease relationship and can be reduced by increasing the sample size. On the other hand, systematic error or bias reflects a problem of validity of the study and arises because of any error resulting from methods used...

Scientific literature may be biased because of the internal validity of studies being compromised by different forms of measurement error, and/or because of the selective reporting of positive and 'statistically significant' results. While the first source of bias might be prevented, and in some cases corrected to a degree, the second represents a pervasive problem afflicting the medical litera...