# Statistical Biases: General Idea & Selection Bias

by Raywat Deonandan, PhD
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Slides 04 CausationBiasIdeaSelection Epidemiology.pdf
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Hello and welcome to epidemiology. In this lecture we are going to start the process of understanding bias and in my opinion bias is probably the most important idea in epidemiology, because if you don't end up being a health researcher or any kind of scientist for that matter, understanding bias will help you be a smarter, better citizen, it's that important. So in this lecture we are going to understand the basic idea of bias and also start the process of understanding selection bias, which is one type of very common bias. There are lots of different types of biases and we will get through some of them, but right now we're going to talk about selection bias. I want to start by exploring some definitions of bias. One of them is, bias is any systematic error in the design, conduct or analysis of a study that results in a mistaken estimate. And the important qualities of that definition are the systematic aspects of it, the error aspects of it and the fact that it ends up giving you a mistaken or problematic or erroneous conclusion. Another definition is, bias is a systematic error in the epidemiologic study that results in an incorrect estimate. Again, key concepts there, the systematicity and the incorrect conclusion or estimate that results from it all. In my opinion, the best kind of definition has to do with the fact that biases lead to erroneous conclusions. It's impossible to eliminate all aspects of bias from any study, but we strive to minimize that small extent, as well it's not usually possible to control for biases in a post hoc analysis statistically, so it is important that we try to make sure that bias doesn't exist as much as we can in the design of...

The lecture Statistical Biases: General Idea & Selection Bias by Raywat Deonandan, PhD is from the course Statistical Biases. It contains the following chapters:

• What is Bias?
• Selection Bias
• Non-response Bias
• Healthy Worker Effect
• Loss to follow-up bias
• Berkson Bias
• Learning Outcomes

### Included Quiz Questions

1. Selection bias
2. Berkson's bias
3. Confounding
1. Loss to follow-up bias
2. Berkson's bias
1. Selection bias
2. Berkson's bias

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