Chapter 2 Descriptive Statistics 2.1 Frequency Distributions and Their Graphs

I. Frequency Distributions Frequency Distribution: a table that shows classes or intervals of data with the number of entries in each class Frequency: the number of entries in a class

ClassFreq How many classes? What are the frequencies? Lower Class Limit: smallest value in a class Upper Class Limit: largest value in a class Class Width: the difference between lower (or upper) limits of consecutive classes Range: the difference between the maximum and minimum data entries

Guidelines for Constructing a Frequency Distribution from a Data Set 1.Choose a number of classes. It should be between 5 and Find the class width by dividing the range by the number of classes and rounding up. If it is a whole number add 1. 3.Find the class limits. Start with the smallest data value as the first lower limit. Then add the class width to get the next lower limit. Then go back and fill in the upper limits. (Classes cannot overlap!)

Guidelines for Constructing a Frequency Distribution from a Data Set (continued) 4.Take a tally by going through each data value and making a mark in the appropriate column. 5.Count the tallies to find the frequencies. Now let’s look at an example. Turn to page 35, example 1.

Now you try! Page 45 #23 ClassTallyFreq.

Now that you got that, we are going to add more columns! Midpoint: (lower limit + upper limit) / 2 Relative Frequency: (class frequency) / (total sample size). Can be a fraction, decimal, or percent that should all add up to 1 or 100%. Cumulative Frequency: the sum of the frequency for that class and all previous classes.

Turn to page 37 and look at example 2. Now add these 3 columns to pg45 #23 from earlier… ClassFMPRFCF

HOMEWORK Page 45 #24 Your frequency distribution should have 6 columns when it’s done! Tip: USE PENCIL