L How to construct a Frequency distribution 1. Number of classes Choose an approximate number of classes for your data Sturges rule can help 2. Estimate the class interval Divide the approximate number of classes(from Step 1)into the range of your data to find the approximate class interval, where the range is defined as the largest data value minus the smallest data value 3. Determine the class interval Round the estimate(from Step 2)to a convenient value C 2002 The Wadsworth Group
How to Construct a Frequency Distribution 1. Number of classes Choose an approximate number of classes for your data. Sturges’ rule can help. 2. Estimate the class interval Divide the approximate number of classes (from Step 1) into the range of your data to find the approximate class interval, where the range is defined as the largest data value minus the smallest data value. 3. Determine the class interval Round the estimate (from Step 2) to a convenient value. © 2002 The Wadsworth Group
l How to construct a Frequency Distribution, cont 4. Lower Class limit Determine the lower class limit for the first class b selecting a convenient number that is smaller than the lowest data value 5. Class Limits Determine the other class limits by repeatedly adding the class width (from Step 2 )to the prior class limit, starting with the lower class limit (from Step 3) 6. Define the classes Use the sequence of class limits to define the classes C 2002 The Wadsworth Group
How to Construct a Frequency Distribution, cont. 4. Lower Class Limit Determine the lower class limit for the first class by selecting a convenient number that is smaller than the lowest data value. 5. Class Limits Determine the other class limits by repeatedly adding the class width (from Step 2) to the prior class limit, starting with the lower class limit (from Step 3). 6. Define the classes Use the sequence of class limits to define the classes. © 2002 The Wadsworth Group
l Converting to a relative Frequency distribution 1. Retain the same classes defined in the frequency distribution 2. Sum the total number of observations across all classes of the frequency distribution 3. Divide the frequency for each class by the total number of observations forming the percentage of data values in each class o 2002 The Wadsworth Group
Converting to a Relative Frequency Distribution 1. Retain the same classes defined in the frequency distribution. 2. Sum the total number of observations across all classes of the frequency distribution. 3. Divide the frequency for each class by the total number of observations, forming the percentage of data values in each class. © 2002 The Wadsworth Group
M Forming a cumulative relative Frequency distribution 1. List the number of observations in the lowest class 2. Add the frequency of the lowest class to the frequency of the second class. record that cumulative sum for the second class 3. Continue to add the prior cumulative sum to the frequency for that class, so that the cumulative sum for the final class is the total number of observations in the data set o 2002 The Wadsworth Group
Forming a Cumulative Relative Frequency Distribution 1. List the number of observations in the lowest class. 2. Add the frequency of the lowest class to the frequency of the second class. Record that cumulative sum for the second class. 3. Continue to add the prior cumulative sum to the frequency for that class, so that the cumulative sum for the final class is the total number of observations in the data set. © 2002 The Wadsworth Group