Section 1.1 Part 4 AP Statistics September 8, 2008 CASA

AP Statistics, Section 1.1, Part 42 Using Percents It is sometimes difficult to compare the “straight” numbers. For example:  Ty Cobb in his 24 year baseball career had 4,189 hits. Pete Rose also played for 24 years but he collected 4,256 hits. Was Pete Rose a better batter than Ty Cobb?

AP Statistics, Section 1.1, Part 43 Using Percents Ty Cobb had a career batting average of.366. (He got a hit 36.6% of the time) Pete Rose had a career batting average of.303. Comparing the percentage, we get a clearer picture.

AP Statistics, Section 1.1, Part 44 Relative Frequency When constructing a histogram we can use the “relative frequency” (given in percent) instead of “count” or “frequency” Using relative frequency allows us to do better comparisons. Histograms using relative frequency have the same shape as those using count.

AP Statistics, Section 1.1, Part 45 Finding Relative Frequency For each count in a class, divide by the total number of data points in the data set. Convert to a percentage.

AP Statistics, Section 1.1, Part 46 Finding Relative Frequency ClassFrequency Total43

AP Statistics, Section 1.1, Part 47 Finding Relative Frequency ClassFrequencyRelative Frequency /43=4.7% /43=14.0% /43=30.2% /43=27.9% /43=16.3% /43=7.0% Total43

AP Statistics, Section 1.1, Part 48 Histograms

AP Statistics, Section 1.1, Part 49 Finding Cumulative Frequency ClassFrequencyRelative Frequency Cumulative Frequency /43=4.7% /43=14.0% /43=30.2% /43=27.9% /43=16.3% /43=7.0%43 Total43

AP Statistics, Section 1.1, Part 410 Finding Relative Cumulative Frequency ClassFrequencyRelative Frequency Cumulative Frequency Relative Cumulative Frequency /43=4.7% /43=14.0%88/43=18.6% /43=30.2%2121/43=48.8% /43=27.9%3333/43=76.7% /43=16.3%4040/43=93.0% /43=7.0%4343/43=100% Total43

AP Statistics, Section 1.1, Part 411 Percentiles “The pth percentile of a distribution is the value such that p percent of the observations fall at or below it.” If you scored in the 80 th percentile on the SAT, then 80% of all test takers are at or below your score.

AP Statistics, Section 1.1, Part 412 Percentiles ClassRelative Cumulative Frequency /43=4.7% /43=18.6% /43=48.8% /43=76.7% /43=93.0% /43=100% Total It is easy to see the percentiles at the breaks. “A 64 year old would be at the 93 rd percentile.” What do you do for a 57 year old?

AP Statistics, Section 1.1, Part 413 Ogives (o-JIVE) or “Relative Cumulative Frequency Graph” ClassRelative Cumulative Frequency /43=4.7% /43=18.6% /43=48.8% /43=76.7% /43=93.0% /43=100% Total

AP Statistics, Section 1.1, Part 414 Time Plots Time (measured in seconds, days, months, years, etc.) is always on the x- axis. Use time plots to see trends related to time like…  Seasonal variation  Growth trends

AP Statistics, Section 1.1, Part 415 Assignment Exercises 1.19 – 1.29 odd, The Practice of Statistics.