Stat 217 – Day 6 Tests of Significance

Quiz 1 Notes Solutions posted in PolyLearn  Grading notation (c) the question I intended (d) make sure put it in context (“of the time”)  Use the percentage or proportion

Last Time Using observed sample data to evaluate a claim about the general process  Is this evidence that students tend to put Tim on the left?  Is this evidence that Sarah does better than guessing? Idea: Look at results that do happen “by chance alone” to see whether our observed data are consistent with that pattern

Example 1: Helper/Hinderer Trying to decide between 1. Infants do evaluate individuals as appealing or aversive based on their actions 2. Infants don’t have a genuine preference and these 16 just happened to pick the helper toy more often

If infants are picking at random Meaning equally between the two toys in the long run

Small p-value : It would be very unlikely to have 14 (or more) picking the helper toy if all 16 infants were picking blindly between the two toys Conclusion: Strong evidence against the null hypothesis in favor of the alternative  Strong evidence these infants (in the long run) have a genuine preference for the helper toy

Mickelson Null hypothesis:  =.418 (his probability of a putt is the same as golfers’ overall) Alternative hypothesis: :  <.418 (Phil has a lower probability of other golfers)

Mickelson If Phil’s probability of a 10-foot putt was.418, we’d expect to see him make 7 or fewer in about 6% of repetitions of 28 putts by chance alone A p-value of.064 is weak evidence that Phil’s long-run probability of putt is lower than.418.  Phil is a “statistically significantly” worse putter.

“Survey” A campus legend tells the story of two friends who told their professor that they got a flat tire returning to town and missed the exam. The professor agreed to give them a make- up exam. The first question (worth 5 points) was easy, but the second question worth 95 points, asked “Which tire was it?”

Data Collection If you have to choose a hypothetically flat tire, which of the four tires would you say went flat? Left frontRight front Left rearRight rear

To Do Reading3 in PolyLearn Reading4 in PolyLearn Submit Lab 1 at beginning of class