AP Statistics Free Response Questions Posted!

You can review the questions from this year’s AP Statistics exam here. My responses are here. Disclaimer: this is my own work, based on my own understanding of the questions. I do not guarantee that all responses would be awarded full credit (though I usually do fairly well!). Moreover, I tend to be very thorough with my responses, more than the AP rubrics generally require (especially with the hypothesis test question). Do not be nervous if you did not give quite as much detail as me.

AP Statistics Exam Final Thoughts

Your AP Statistics Test is Thursday afternoon. Be outside York Lecture Hall by 11:50 with your calculator and pencils (non-mechanical, remember!). Do not bring your backpack, bag, or your cell phone (or any other “smart” device like watches); find somewhere to put them. You may bring a snack or water, but it must be in clear packaging and you may not have it at your desk with you. Do not expect to leave until at least 4:00!

See this post from before with the archive of review materials.

Things you should be sure to remember (these are my thoughts, see pages 608-610 of your review book for some further points):

  • The formulas for the mean/standard deviation of a sampling distribution of means and a sampling distribution of proportions are on your formula sheet. Whenever you’re being asked to calculate a mean or a standard deviation, check to see if it’s one of these.
    • Related: Pay attention to which standard deviation you are being asked to calculate. The standard deviation of a sample is not the same thing as the standard deviation of a sampling distribution.
  • Probability questions will come in three categories
    • Direct calculation based on a finite sample space (like rolling dice). Write out all the possible outcomes and count which ones are the ones you want. This also includes two-way tables. Don’t try to use fancy formulas for those; just count!
    • Number of successes questions. For example: “how many model E cars would you expect to see in a 2000 car sample?” or “what’s the probability that at least one out of the four drivers is speeding?” These are applications of the binomial probability model and should be calculated appropriately using the formulas on your sheet.
    • Number of trials questions. For example: “how many chips would you expect to need to check before finding a defective one?” or “what’s the probability that the 5th donor is the first with Type-B blood?” These are applications of the geometric probability model. The formulas are not on your sheet, and so you should memorize them: q^(K-1)*p for a general probability and 1/p for the expected value.
  • Know how to combine the standard deviations of two or more random variables. Remember: variances always add.
  • Know how to read the regression output of a linear association. What do “constant,” “estimate/coefficient,” “prob” all mean? Refer to pages 111-112 in your review book or page 729 in your textbook.
  • Know the difference between stratified and cluster sampling and how to identify/use them. Also remember that for a simple random sample every possible sample has the same chance of being chosen.
  • Know the important conditions for each of the inference procedures:
    • Everything: Random Condition
    • Any z-test: Success/failure condition
    • Any t-test: Nearly Normal/Large Enough condition
    • Any chi-square test: Expected cell frequency condition
    • Any 2-sample/2-proportion test: groups are independent from each other.
    • Also: know when to use a 2-sample t-test vs. a matched pairs t-test
  • Be mindful of notation. Don’t use x-bar when you should be using µ. Don’t use p when you should use p-hat.
    • Related: No Naked Numbers! Every number included in any response should have a label somewhere (mean, standard deviation, p-value, etc.)
  • Context, context, context. Always frame your answers in the context of the situation. Don’t say, “I am 95% confident that the true proportion of success is between 22% and 37%.” Say instead: “I am 95% confident that the explosive sensor will accurately detect hidden explosives 22% to 37% of the time.”
  • Be complete with your responses. When choosing between two possibilities in a free response question, explain why one possibility is wrong and why the other one is correct. When asked to compare two distributions, make explicit comparative statements, e.g, “Group 1 is centered at around 12, which is greater than Group 2, which is centered around 7”
  • At the same time, don’t give more information than is requested. If the question asks you to describe the shape of a distribution of data from a histogram, don’t discuss center and spread. If the question asks you to explain your randomization procedure for an experiment, you don’t need to explain what the response variable is, how you’re going to measure it, and what a statistically significant outcome would look like. If the question asks you to merely calculate a confidence interval, you don’t have to interpret it.

AP Statistics Pre-exam breakfast

Ms. Seifert and I would like to invite you to a pre-exam breakfast and review session in her room, H213, on Thursday. We’ll start things up around 8:40 for those of you who don’t have 1st period free, and we’ll spend 1st period hanging out and answering any lingering, last-minute questions you may have.

We plan to get bagels, but if you have dietary restrictions (gluten free, vegan, etc.) please indicate them on this form by the end of the day!

AP Statistics Review Phase 1

Our review for the AP Exam has started. Phase 1 will take us to the practice AP exam on Thursday, April 25th at 8:00 am in York Lecture Hall. More details will be posted soon.

The review calendar for the first part can be found here. Most of this review will be done out of the Barron’s review books you have obtained, so plan on bringing those to class for the first several days of review. There is a lot more to these books than we plan to do in class, so please continue to work through the practice tests and other chapters on your own.

AP Exam Pre-Administration Sessions

All students taking the AP Statistics exam (and any other AP exam) must attend a pre-administration session to complete some necessary paperwork. The sessions are as follows (and all of them take place in York Lecture Hall):

  • Tuesday, 4/9: Periods 0, 1, 3, 7, and after school
  • Wednesday, 4/10: Periods 4, 5, 8
  • Thursday, 4/11: Periods 0, 2, 6, and after school

Sessions start immediately at the start of the period, and you will not be allowed in if you are late. Expect to stay the full period.