Stat 217 – Day 9 Sampling

Recap (Lab 1) Observational unit = Sarah’s attempts (n = 8) Research hypothesis:Can Sarah solve problems  Research conjecture: Sarah can correctly match most of the pictures Alternative hypothesis (Ha):  >.5 Null hypothesis (Ho):  >.5 p-value = probability she gets 7 or more right when she is just guessing Small p-value (.035)  Evidence against the null hypothesis

Recap (Investigation 1) Task one (matching variables to graphs)  Graded on fullness of explanation (e.g., how consistent, whether description eliminated other choices)

Recap (Investigation 1) Turns out JMP puts the categories in alphabetical order  Separating bars helps indicate have a categorical variable (no “in between” values) or “discrete” data (e.g., number of siblings) Comparing quantitative distributions  Shape = symmetric?  Center = look at mean?  Spread = look at standard deviation?

Recap (Quiz 1) There is a journal called Gut?? Observational units = Marine’s attempts Variable = whether or not she picks correctly Statistic = 30/33, proportion correct in sample Null hypothesis:  = 1/5 (she’s guessing) Alternative hypothesis:  > 1/5 If Marine was just guessing, would be VERY surprising for her to get as many as 30 correct.

Recap Want to make a claim about the population or the underlying process (e.g.,  =.25,  >.25)  Our strategy is to assume the boring version of the claim (  =.25) and then see whether we have sufficient evidence against that claim in favor of a more interesting claim (  >.25). Today  Two-sided p-values  Normal approximation  Sampling from a population (tomorrow)

To Do Finish Lab 2 Readings in PolyLearn