1. Chapter 2 Describing, Exploring, and Comparing Data
Statistics
Chapter 2
Describing, Exploring, and Comparing Data

2. Section
2.2 notes

3. This chapter looks at important concepts of descriptive statistics where we use different methods to summarize or describe the important characteristics of a set of data.

4. Important Characteristics of Data:
Center – average value that indicates where the middle of the data set is located
Variation – a measure of the amount that the values vary among themselves
Distribution – the shape of the distribution of the data (bell-shaped, uniform or skewed)
Outliers – values that are far away from the other sample values
Time – changing characteristics of the data over time

5. Frequency table lists classes (categories) of values along with frequencies (counts) of the number of values that fall into each class.
Frequency – the number of scores that fall into a particular class

6. Frequency Table:

7. Lower class limits – the smallest numbers that can belong to the different classes
Upper class limits – the largest numbers that can belong to the different classes
Class midpoints – the midpoints of the classes (duh!), found by adding lower class limit to upper class limit and dividing by 2

8. Lower class limits

9. Upper class limits

10. Class midpoints

11. Class width – the difference between two consecutive lower class limits or two consecutive upper class limits
If you are starting with the original data, class width is found by subtracting the lowest value from the highest value and dividing by the number of classes you want to include (should be between 5 and 20)

12. Class width

13. Relative frequency – found by dividing the class frequencies by the total of all frequencies
Cumulative frequency – the sum of all the frequencies for that class and all previous classes

14. Example:
p.39 #17 – the weights of bears