# Sampling vs. Selection Bias?

Discussion in 'Step I' started by PsychoDan, May 3, 2006.

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1. ### PsychoDanJunior Member 2+ Year Member

38
0
Apr 18, 2006
Does anyone have a good grasp on bias that cna explain the difference between sampling vs. slection bias? Sampling bias is obtaining results that are not generalizable to the population because the sample is not representative. How is selection bias different?

Thanks!

3. ### Texagg2003New Member

2
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Sep 22, 2003
Houston, Tx
My take on selection bias is having a study consisting of volunteers. Therefore you are already biased upon having only people who would volunteer for the study. In the group of volunteers - they can still be a good representative group of the general population so no sampling bias. Is this right?

4. ### DrPakSenior Member 5+ Year Member

183
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Nov 19, 2005
They are the same thing.

As you said, sampling bias is when you choose a sample that is not representative of the general population, and thus does not give you results you could extrapolate to hold true for the entire population.

For instance, if you were to examine the incidence of heart disease in a city and got your data by interviewing people entering or leaving a mall, you'd miss out all the REALLY sick coronary patients because many of them wouldn't be found moseying around a mall - more likely they'd be confined to their homes at best, or in the hospital at worst.

When your method of selecting the representative sample is wrong, you end up with the sampling\selection bias. The word "sampling" being used as a verb in this context.