12.2 Frequency Distributions and Statistical Graphs 771 Often data are grouped in classes to provide information about the distribution that would be difficult to observe if the data were ungrouped. Graphs called histograms and frequency polygons can be made of grouped data, as will be explained later in this section. These graphs also provide a great deal of useful information. When data are grouped in classes, certain rules should be followed. Example 1 Frequency Distribution The number of children per family is recorded for 64 families surveyed. Construct a frequency distribution of the following data: 0 1 1 2 2 3 4 5 0 1 1 2 2 3 4 5 0 1 1 2 2 3 4 6 0 1 2 2 2 3 4 6 0 1 2 2 2 3 4 7 0 1 2 2 3 3 4 8 0 1 2 2 3 3 5 8 0 1 2 2 3 3 5 9 Solution Listing the number of children (observed values) and the number of corresponding families (frequency) gives the following frequency distribution. Number of Children (Observed Values) Number of Families (Frequency) 0 8 1 11 2 18 3 11 4 6 5 4 6 2 7 1 8 2 9 1 64 Eight families had no children, 11 families had one child, 18 families had two children, and so on. Note that the sum of the frequencies is equal to the original number of pieces of data, 64. 7 Now try Exercise 11 “Statistical thinking will one day be as necessary for efficient citizenship as the ability to read and write.” H. G. Wells RULES FOR DATA GROUPED BY CLASSES 1. The classes should be the same “width.” 2. The classes should not overlap. 3. Each piece of data should belong to only one class. PROCEDURE Answer: There are 6 F’s. RECREATIONAL MATH Can You Count the F’s? Statistical errors often result from careless observations. To see how such errors can occur, consider the statement below. How many F’s do you count in the statement? The answer is upside down below. FINISHED FILES ARE THE RESULT OF YEARS OF SCIENTIF- IC STUDY COMBINED WITH THE EXPERIENCE OF YEARS.
RkJQdWJsaXNoZXIy NjM5ODQ=