Bias In Statistics BY: JACKIE SARTORELLI & ANDREW CROSBY

What Is Bias?  A method is biased if it has a tendency to produce an untrue value by systematically favoring some outcomes over others.

Nonresponse Bias  Nonresponse Bias is a sampling bias that occurs when people selected to participate in a survey fail to respond or refuse to do so.  This bias is bad to use because it is not taking account of those that did not respond to the survey.  Example) When a survey is sent out in the mail and people choose not to respond.

Wording Bias  Occurs when a question is asked with persuasion or is “loaded”.  This method is not a good method to use because it can persuade people to answer in line with what’s implied.  Example) Only cool and smart people like school, do you like school?

Under-coverage  Occurs when people are not given a chance to respond.  This method is bad because it does not accurately represent the entire population in its data.  Example) When a survey is sent out to only those with landline telephones.

Voluntary Response Bias  A sampling bias that occurs when people who generally have strong feelings about the results participate (self-selected volunteers)  This bias is bad because it is only taking account of those that choose to participate, rather than the whole population.  Example) When American Idol asks the audience to vote for their top pick and those that choose to vote do.

Convenience Sampling  A sampling bias that occurs when people are chosen because they are the easiest, or most convenient to reach.  A bad method to use because the results will not account for the whole population, only those that were chosen and it does not allow people to be equally chosen.  Example) When a surveyor in a mall asks those passing by to take a survey.

Quiz  What kind of bias occurs when someone adds a review on Yelp?  What kind of bias occurs when a surveyor asks, “Most people that drink soda are unhealthy and overweight, do you drink soda?”  What kind of bias occurs when only people who have an address are asked to respond?  Can you give an example of nonresponse bias?  How about convenience bias?