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Explore the intricacies of statistical biases in data collection methods and the implications on study outcomes. Delve into deliberate reporting, respondent behavior, and sampling techniques. Learn how to navigate through pitfalls and maintain data integrity.
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Statistic for the day:The number of countries that have claimed to have discovered America: 11 Assignment: Read Chapter 3 Exercises p. 44-46: 1, 2, 3, 6, 7, 8, 10 These slides were created by Tom Hettmansperger and in some cases modified by David Hunter
Change is good? • Questions: • 1. Do PSU women carry more change than men? • 2. Is there a greater proportion of women who carry • change than men? • How to formulate question 1 in statistical terms: • Is the mean amount of change carried by PSU women • greater than the mean amount of change carried by men? • Take samples of change from women and men and • compare the sample means.
Pitfalls and issues encountered in collecting data both as • categorical data in surveys and as measurements in • experiments. (Chapter 3) • A student did a mini-project on deliberate bias in a stat • course. She asked two forms of the same question: • If you found a wallet with $100 in it on the street, would • you keep it? • If you found a wallet with $100 in it on the street, would • you do the honest thing and return it or would you keep it? Deliberate Bias • Of 10 people asked question 1, 8 said they would keep it. • Of 10 people asked question 2, all 10 said they would return it.
Desire to please • People want to please the interviewer. • People often give socially acceptable answers, not the truth. • In a comparison of self reported cigarette consumption and • actual consumption, it was found that: • In 1964, the year of the Surgeon General’s report • self reporting was roughly 75% of the actual consumption • By 1975 self reporting has dropped to 67% of actual • consumption. • Self reporting determined by national surveys and actual • consumption determined by sales and production.
Asking the uninformed People don’t like to appear uninformed and will often give answers when they don’t know what they are talking about. Pollsters should always provide “don’t know” option. • When the American Jewish Committee studied • American’s attitudes toward various ethnic groups, • roughly 30% rated (fictional) Wisians in social • standing above 6 other real groups, including • Mexicans, Vietnamese and African blacks. • p33 of the text
How often do you normally go out on a date? • about ___ times per month. • How happy are you with life in general?
Ordering of questions • Consider the following two questions: • How happy are you with life in general? • How often do you normally go out on a date? • about ___ times per month. • When asked in the above order there was no correlation • between the answers (correlation coefficient = -.12) • When asked in reverse order, the correlation coefficient • jumped up to .66
Confidentiality and anonymity Confidential answer: Respondent is known but the answer is kept secret. Anonymous answer: Respondent is not known. • HIV testing is sometimes done anonymously by giving • the person being tested an identifying number that is used • in retrieving the results. • In surveys, people often want to be anonymous. But that • makes it harder to follow up on non-respondents. • Randomized response sampling was devised to provide • anonymity. Recall the ‘pot smoking question’ in class.
Open and closed form questions A closed question is one in which respondents are given a list of possible answers to pick from. An open question is one in which respondents are allowed to answer in their own words. (Difficulty: results are hard to summarize.) The problem is that the closed question responses may not even be mentioned by people responding to the open version of the question. Solution: Do a small pilot study with open questions and pick the most common responses for the closed questions.
A trick in advertising (Example 4 p39 of the text) • Advertisement for Triumph cigarettes: “Triumph beats • Merit—an amazing 60% said Triumph tastes as good • or better than Merit.” • Three choices were given to the respondents: • Prefer Triumph • Prefer Merit • No preference • 36% preferred Triumph • 40% preferred Merit • 24% no preference • Statement in the advertisement is true but Merit is • preferred!!
