Final answer:
A main form of selection bias is sampling bias, where certain members of a population are less likely to be included in a study sample, leading to unrepresentative results. Social desirability bias, exemplified by the "Bradley effect," is another type where participants misreport their true opinions to appear socially acceptable.
Step-by-step explanation:
A main form of selection bias occurs when the sample chosen for a study does not accurately represent the population being researched. This leads to results that may incorrectly generalize the findings. One common type of selection bias is sampling bias, where certain members of the population have a lower chance of being included in the study due to the sampling method used.
For example, if a survey were to be conducted only during noon lunchtime hours, it would be biased against students who do not have lunch at that time. Similarly, internet surveys can also contain selection bias because participation is optional, and those who choose to respond may have different characteristics compared to those who don't. This kind of bias can significantly impact the validity of a study's conclusions.
Another form of selection bias is the social desirability bias. An example of this is the "Bradley effect," where polling results were skewed because respondents did not accurately report their voting intentions, likely due to wanting to appear unbiased against a minority candidate despite their true preferences.