1. Measures of Central Tendency PS Algebra I

2. Objectives Given a set of data, be able to find the following: 1) mean* 2) median* 3) mode* 4) range 5) first and third quartiles 6) interquartile range

3. Mean the “mean” of the data set is the average add up all of the numbers in the set and then divide by the number of numbers in the set

4. Median the “median” of a data set is the middle value when the numbers in the set are placed in numerical order two cases: 1) for sets with an odd number of numbers, pick the number right in the middle 2) for sets with an even number of numbers, add up the two numbers in the middle and then divide the sum by two

5. Mode the “mode” of a data set is the most occurring number(s) in the set if more than one number occurs the most, all of those numbers make up the mode if every number in the set is different (only appears once), then there is no mode

6. Range the “range” measures the amount of dispersion or “spread” of the numbers in a data set formula: highest number in the set (maximum) – lowest number in the set (minimum)

7. First and Third Quartiles a “quartile” is just the median for only one half of the data set first quartile: median for the first half of the set third quartile: median for the second half of the set if there is an odd number of numbers in the set, you must throw out the actual median in order to create the halves

8. First and Third Quartiles in a typical data set: 1) roughly 25% of the data falls below the first quartile 2) roughly 25% of the data falls above the third quartile 3) roughly 50% of the data falls between the first and third quartiles

9. Interquartile Range the “interquartile range” measures the amount of dispersion or spread of the numbers between the first and third quartiles formula: third quartile – first quartile

10. On the calculators…

11. Procedure continued: 4) Press STAT again and then move the cursor over to CALC 5) In the CALC menu, select Option 1 (1-Var Stats) 6) Move the cursor down to Calculate and press ENTER

12. On the calculators…

13. Let’s find some info! Given the following data sets, find the following: 1) mean 2) median 3) mode 4) range 5) first and third quartiles 6) interquartile range

14. Let’s find some info! A) 23, 42, 35, 51, 37, 39, 50, 25, 51 B) 14, 20, 18, 5, 19, 23, 23, 18, 30, 25 C) 13, 30, 45, 21, 18, 34, 23, 40, 8