We discuss the possible reasons for their findings (for example, selection bias and low (20%) statistical power to detect mortality endpoints), and also perform an update of our previous meta-analysis with the addition of Heininger and colleagues' study to verify whether the higher mortality rate with CMV holds.
Some biases, for example selection bias and some forms of measurement error can, affect the results in a direction that is difficult to predict [ 6].
However, cluster-randomized trials also have limitations, for example, selection bias can occur and withdrawal drop-out of whole clusters may seriously affect the validity of the results.
For example, selection for reproductive assurance and colonisation advantage due to mate limitation during range expansions, or as a result of high population turnover in metapopulations, can drive transitions to self-fertilisation strategies [ 8- 10].
If Ireland were to complete a double over the All Blacks in Dublin on Saturday week, for example, selection for next year's British and Irish Lions tour will assume a very different hue.
For example, selection for better lactation ability and persistence, primarily over the past 5,000 years, has increased milk production [ 1, 7].
For example, selection for resistance to paclitaxel and epirubicin resulted in a dose-dependent increase in the expression of the ABCB1 drug transporter (P-glycoprotein), without a significant change in the expression of any other drug transporter.
However, the limitations of this method (for example, selection bias) need to be acknowledged and the implications for interpretation considered.
For example, selection varies across genes as a consequence of protein function and gene expression patterns [ 1].
For example, selection bias and/or systematic error may occur because the cases were from the hospital and the controls were from the community.
For example, selection for translational efficiency is one possible explanation for the connection between gene expression and codon usage bias [ 25].
