1. Statistical Studies Sampling Methods

2. Identifying Bias Biased sample might not really represent the entire population, so we want to avoid selecting one. Biased sample might not really represent the entire population, so we want to avoid selecting one.

3. Identifying Bias non-response bias Self-selected respondents tend to have stronger opinions on subjects than others and are more motivated to respond, phone-in and online polls also tend to be poor representations of the overall population.

4. Identifying Bias non-response bias: if researchers simply hand out questionnaires on a street corner and ask people to fill them out and then mail them in, most people will just throw the questionnaires away. Only people who are really interested in the subject will bother to send them in, and those might also be the people who are more likely to answer the questions a certain way

5. Identifying Bias Several ways to spot biased questions: They may use polarizing language, words and phrases that people associate with emotions: Is it right that farmers murder animals to feed people? How much of your time do you waste on TV every week?

6. Identifying Bias Several ways to spot biased questions: They may refer to a majority or to a supposed authority: Would you agree with the American Heart and Lung Association The question may be phrased so as to suggest the person asking the question already knows the answer: It’s OK to smoke so long as you do it on your own, right?

7. Identifying Bias Several ways to spot biased questions: The question may be phrased in ambiguous way (often with double negatives) which may confuse people: Do you reject the possibility that the moon landings never took place?

8. Identifying Bias The overall design of a survey can be biased in other ways. Question order can play a role: For example, a survey may contain several questions on people’s attitudes to cigarette smoking. Then, if the question “What, in your opinion, are the three biggest threats to public health today?”