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

Section 2.2 notes

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.

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

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

Frequency Table:

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

Lower class limits

Upper class limits

Class midpoints

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)

Class width

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

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