Chapter 2 Frequency Distributions and Graphs

Chapter 2 Frequency Distributions and Graphs

Outline 2-1 Organizing Data 2-2 Histograms, Frequency Polygons, and Ogives 2-3 Other Types of Graphs

Objectives Organize data using a frequency distribution. Represent data in frequency distributions graphically, using histograms, frequency polygons and ogives. Represent data using bar graphs, Pareto charts, time series graphs, pie graphs, and dotplots. Draw and interpret a stem and leaf plot.

A frequency distribution is the organization of raw data in table form, using classes and frequencies. Each raw data value is placed into a quantitative or qualitative category called a class. The frequency of a class is the number of data values contained in a specific class.

1. Categorical 2. Grouped 3. Ungrouped

Twenty-five army inductees were given a blood test to determine their blood type. The data set is A B B AB O O O B AB B B B O A O A O O O AB AB A O B A Construct a frequency distribution for the data.

Solution: Class A B O AB Total Frequency 5 7 9 4 25 Percent 20% 28% 36% 16% 100%

These data represent the record high temperatures in degrees Fahrenheit for each of the 50 states. Construct a grouped frequency distribution for the data, using 7 classes. 112 100 127 120 134 118 105 110 109 112 110 118 117 116 118 122 114 114 105 109 107 112 114 115 118 117 118 122 106 110 116 108 110 121 113 120 119 111 104 111 120 113 120 117 105 110 118 112 114 114

Solution: R = H - L = 134 100 = 34 Class width = R / number of classes = 34 / 7 = 4.9 5 Class Limits 100 104 105 109 110 114 115 119 120 124 125 129 130 134 Class Boundaries 99.5 104.5 104.5 109.5 109.5 114.5 114.5 119.5 119.5 124.5 124.5 129.5 129.5 134.5 Total Frequency 2 8 18 13 7 1 1 50

A cumulative frequency distribution is a distribution that shows the number of data values less than or equal to a specific value (usually an upper boundary). Less than 99.5 Less than 104.5 Less than 109.5 Less than 114.5 Less than 119.5 Less than 124.5 Less than 129.5 Less than 134.5 Cumulative Frequency 0 2 10 28 41 48 49 50

The data represent the number of miles per gallon that 30 selected four-wheel-drive sport utility vehicles obtained in city driving. Construct a frequency distribution, and analyze the distribution. 12 17 12 14 16 18 16 18 12 16 17 15 15 16 12 15 16 16 12 14 15 12 15 15 19 13 16 18 16 14

Solution: R = H - L = 19 12 = 7 Class Limits 12 13 14 15 16 17 18 19 Class Boundaries 11.5 12.5 12.5 13.5 13.5 14.5 14.5 15.5 15.5 16.5 16.5 17.5 17.5 18.5 18.5 19.5 Total Frequency 6 1 3 6 8 2 3 1 30

Cumulative frequency distribution Less than 99.5 Less than 104.5 Less than 109.5 Less than 114.5 Less than 119.5 Less than 124.5 Less than 129.5 Less than 134.5 Cumulative Frequency 0 2 10 28 41 48 49 50

The histogram is a graph that displays the data by using contiguous vertical bars (unless the frequency of a class is 0) of various heights to represent the frequencies of the classes. Construct a histogram to represent the data shown for the record high temperatures for each of the 50 states (see Example 2-2).

The frequency polygon is a graph that displays the data by using lines that connect points plotted for the frequencies at the midpoints of the classes. The frequencies are represented by the heights to of the points. Using the frequency distribution given in Example 2-4, construct a frequency polygon.

Solution: Class Boundaries 99.5 104.5 104.5 109.5 109.5 114.5 114.5 119.5 119.5 124.5 124.5 129.5 129.5 134.5 Midpoints 102 107 112 117 122 127 132 Total Frequency 2 8 18 13 7 1 1 50

The ogive is a graph that displays the cumulative frequencies for the classes in a frequency distribution. Construct an ogive for the frequency distribution described in Example 2-4.

Solution: Less than 99.5 Less than 104.5 Less than 109.5 Less than 114.5 Less than 119.5 Less than 124.5 Less than 129.5 Less than 134.5 Cumulative Frequency 0 2 10 28 41 48 49 50

A bar graph represents the data by using vertical or horizontal bars whose heights or lengths represent the frequencies of the data. The table shows the average money spent by first-year college students. Draw a horizontal and vertical bar graph for the data.

Solution: Electronics $728 Dorm Decor $344 Clothing $141 Shoes $72

A pareto chart is used to represent a frequency distribution for a categorical variable, and the frequencies are displayed by the heights of vertical bars, which are arranged in order from highest to lowest. The data shown here consist of the number of homeless people for a sample of selected cities. Draw and analyze a pareto chart for the data.

Solution:

The purpose of the pie graph is to show the relationship of the parts to the whole. A pie graph is a circle that is divided into sections or wedges according to the percentages in each category of the distribution. This frequency distribution shows the number of pounds each snack food eaten during the super bowl. Construct a pie graph for the data.

Solution: Degrees = f/n * 360 o Potato chips 11.2/30*360 o =134 o Tortilla Chips 8.2/30*360 o =98 o Pretzels 4.3/30*360 o =52 o Popcorn 3.8/30*360 o =46 o Snack nuts 2.5/30*360 o =30 o

% = f/n * 100 Potato chips 11.2/30*100=37.3% Tortilla Chips 8.2/30*100=27.3% Pretzels 4.3/30*100=14.3% Popcorn 3.8/30*100=12.7% Snack nuts 2.5/30*100=8.3%

A time series graph represents data that occur over a specific period of time. The data show the percentage of U.S. adults who smoke. Draw and analyze a time series graph for the data. Year 1970 1980 1990 2000 2010 Percent 37 33 25 23 19

Solution:

The stem and leaf plot is a method of organizing data and is a combination of sorting and graphing. A stem and leaf plot is a data plot that uses part of the data value as the stem and part of the data value as the leaf to form groups or classes. At an outpatient testing center, the number of cardiograms performed each day for 20 days is shown. Construct a stem and leaf plot for the data.

Solution: 25 31 20 32 13 14 43 02 57 23 36 32 33 32 44 32 52 44 51 45

Time Time Series Graph Qualitative Data Bar Graph Pareto Chart Pie Graph Quantitative Data Histogram Frequency Polygon Ogive

1. Cut off (or truncate) the y axis.

2. Exaggerate a one-dimensional increase by showing it in two dimensions.

3. Omit labels or units on the axes of the graph. 4. All graphs should contain a source for the information presented.