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Selection bias is another bias that could have been included in the endgame. Selection bias is a general term used to describe a group of biases and effects that result in a sample that is systematically different from the population it is intended to represent. Non-response bias and volunteer bias belong to this group1.
Participants were recruited from the community if they were aged 50 years or over and had a clinical and radiographic diagnosis of mild to moderately severe medial knee osteoarthritis. In total, 103 individuals were randomised to lateral wedge insoles and 97 to flat insoles2.
If there was information about in total, how many were eligible and invited to take part in the trial, and how many accepted the invitation? If the number of subjects invited and no. of subjects accepted the invitation were different, the sample would have been prone to non-response bias. Non-response bias would have occurred if the women who accepted the invitation were systematically different from those who did not1. The women who accepted the invitation would have been expected to be different from those who did not, not least in their motivation to take part in the trial1. However, any differences in characteristics (including sociodemographics and prognostic factors) would be difficult to quantify because limited information, if any, would be available for those who refused to be part of the trial. Non-response bias should not be confused with response bias, or volunteer bias1. Non-response bias focuses on the potential differences between the non-responders and responders originally invited to be part of the sample, whereas volunteer bias considers the potential differences between those who volunteered and the population1.
References:
1. BMJ 2015;351:h3869
2. BMJ 2011;343:d4176
Competing interests:
No competing interests
17 September 2016
Neeru Gupta
Scientist F
Jugal Kishore (Director Professor and Head, Community Medicine, VMMC and Sufdurjung Hospital).
Bias in clinical trials: Author could have explained the selection bias as well.
Selection bias is another bias that could have been included in the endgame. Selection bias is a general term used to describe a group of biases and effects that result in a sample that is systematically different from the population it is intended to represent. Non-response bias and volunteer bias belong to this group1.
Participants were recruited from the community if they were aged 50 years or over and had a clinical and radiographic diagnosis of mild to moderately severe medial knee osteoarthritis. In total, 103 individuals were randomised to lateral wedge insoles and 97 to flat insoles2.
If there was information about in total, how many were eligible and invited to take part in the trial, and how many accepted the invitation? If the number of subjects invited and no. of subjects accepted the invitation were different, the sample would have been prone to non-response bias. Non-response bias would have occurred if the women who accepted the invitation were systematically different from those who did not1. The women who accepted the invitation would have been expected to be different from those who did not, not least in their motivation to take part in the trial1. However, any differences in characteristics (including sociodemographics and prognostic factors) would be difficult to quantify because limited information, if any, would be available for those who refused to be part of the trial. Non-response bias should not be confused with response bias, or volunteer bias1. Non-response bias focuses on the potential differences between the non-responders and responders originally invited to be part of the sample, whereas volunteer bias considers the potential differences between those who volunteered and the population1.
References:
1. BMJ 2015;351:h3869
2. BMJ 2011;343:d4176
Competing interests: No competing interests