Stat 217 – Day 22 Review

Last Time – Subtle Issues Make sure you have a random sample or interval doesn’t tell you much! Make sure you have a sample!  Don’t need a CI when know parameter Statistical vs. practical significance  Strong evidence vs. big difference Duality of test and confidence interval  Mean vs. most  Fail to reject H 0 vs. it’s true!

Last Time If all else is the same:  Smaller s will have smaller p-value and shorter confidence interval  Larger n will have smaller p-value and shorter confidence interval Using applet  Let me know which procedure  Can ignore Ho, Ha, test statistic, p-value if only need CI.  Inputs required

Format of Exam Can bring two (two-sided) pages of notes that either I gave you or you self-produced  Prepare as if closed book  Work efficiently Still bring calculator Be able to read computer output Be able to carry out calculations using appropriate applets

Types of Calculation Problems 1. Probability calculations for normal distribution  Given mean and standard deviation 2. Probability calculations for a sampling distribution (CLT)  E.g., if  =.2, what is the probability <.1  Sketch (and label) distribution 3. Test of significance (6 steps)  Is there statistically significant evidence that… 4. Confidence interval (4-5 steps)  Estimate the population parameter…

Test of Significance Steps (bottom p. 338) 1. Define parameter in words 2. State Ho and Ha hypotheses about parameter 3. Check technical conditions Be able to sketch sampling distribution if met 4. Calculate test statistic 5. Use technology to determine p-value 6. Make conclusion: evaluate p-value, reject or fail to reject Ho, and answer the research question in context

Confidence Interval Steps 1. Define parameter in words 2. Check technical conditions 3. Use technology to determine the interval 4. Interpret the interval … I’m 90% confident that… 5. If asked, interpret “confidence” without using “confidence”

Showing work By hand: show formula, numbers plugged in Applets: which one, which option (e.g,. “one mean”), numbers plugged in  Normal probability Calculator  Test of Significance Calculator p-value and confidence interval NOT “Simulating confidence intervals”

Types of Interpretation Problems Population vs. sample vs. sampling distribution Interpret probability, confidence interval, confidence level, p-value… Including “what if” Identify appropriate procedures Scope of conclusions (generalizability, causation) Why?

HW Comments Parameter vs. population  Defining parameter (“all” or “population”…)  EV vs. RV Conclusion in English/context  The population mean …  This didn’t happen by chance alone… Two populations/samples  Vs. groups, Vs. “the sample size is large enough”  CI: Which population has higher mean/proportion Direction of subtraction, All negative values implies… Technical conditions  Stating vs. checking  Random sample check!

Common Mistakes Quantitative vs. categorical  Symbols:  vs.  (be able to define in words)  Technical conditions  z-procedures with proportions, t-procedures with means  Don’t combine: “mean proportion” Stating hypotheses about statistic/nothing  H 0 : =.5 Sample size checks  vs. population check. What’s “normal”?  What changes when you increase the sample size… Parameter vs. statistic, sample vs. sampling distn Stopping at “reject Ho” decision…

Advice Work problems, don’t just read them!  Using only notes pages, calculator  Start with a picture  See if you can identify problem type  Think about what each step means  Banish the words IT, proof, data  Add the phrase “of what” and “for what” Learn from/seek clarification of grader comments  HW, labs, TIA activities, etc. Topic summaries, Self-check, Watch Out points

Student Recommended Strategies Study group (visual referent) Old material, homeworks, and practice problems Study in advance, relax day of Study guide, boxed items, watch out sections Doing other (new) problems in text, reading labs Vocabulary Feedback on how to format responses, see where lost points Making the note sheet