Biases in epidemiological studies are of two main types: selection bias and information (or measurement) bias.
To obtain a large contribution due to incomplete follow-back required an implausibly high proportion of missed survival time, and with more plausible values the main factors were selection bias and intrinsically higher mortality.
The main likely biases are selection bias stemming from under-sampling of absentee students and information bias due to the data collection strategy used in the study.
40 All three main types of epidemiologic bias – selection bias, information bias, and confounding – occur in studies of medical databases.
One of the main limitations may be a selection bias for patients subjected to PCI and MTH.
Moreover, only minor differences were found between the main therapies at baseline, making selection bias less likely.
That none of the participants reported a family history of cancer might be a limitation of the main study owing to self selection bias.
We did not identify any significant difference between included and not-included VDP programs regarding their main characteristics, which suggests limited selection bias within the VDP program itself.
We recruited from all the clinics in primary care and from the main secondary care centre to minimise selection bias.
The main potential study limitations are (1) selection bias may exist in the catchment of breast cancer patients in the selected hospitals as no less elite hospitals as comparison were selected from the same regions.
