3. T-tests
• The t-test is used to test hypotheses
about means when the population
variance is unknown (the usual case).
• Developed by Gossett for the quality
control of beer.
• Comes in 3 varieties:
• Single sample, independent samples,
and dependent samples.
4. T-tests
• Single sample t – we have only 1
group; want to test against a
hypothetical mean.
• Independent samples t – we have 2
means, 2 groups; no relation between
groups, e.g., people randomly
assigned to a single group.
• Dependent t – we have two means.
Either same people in both groups, or
people are related, e.g., husband-
5. ANOVA
• Collection of methods
• Analyze differences between group
means
• Generalizes the T-test to more than
two groups
• Within vs. Between groups
13. Pearson’s Chi-Squared
• Osbserved vs. Expected
• Example: Tax lien auctions in DC
• Determine what a “regular” auction
might look like
– Consulted experts
– Looked at collusive and non-collusive
auctions in other jurisdictions
16. What to do?
• We felt it would be lazy to just
describe the patterns
• We wanted to look how frequently the
irregular patterns occurred between
bidders
• Leader vs. Follower analysis
• Pearson’s Chi-Squared Test
18. How to avoid mistakes
• Try to prove yourself wrong
• Run it by your targets
• Ask someone smarter than you
• Make sure you’re doing the correct
test
