CHAPTER 2 ORGANIZING DATA - Cengage

CHAPTER 2 ORGANIZING DATA

HISTOGRAMS (SECTION 2.2 OF UNDERSTANDABLE STATISTICS)

SPSS has two menu options for drawing histograms. The option Graphs Histogram draws a histogram with default choice of boundaries (cutpoints), and the option Graphs Interactive Histogram allows user to define boundaries of the histogram. Histograms may also be drawn through

Analyze Descriptive Statistics Frequencies.

Graphs Histogram

Dialogue Box Responses

Select the variable to draw the histogram.

There are options for giving a title or displaying a normal curve with the histogram.

Click on OK to construct and display the histogram.

Analyze Descriptive Statistics Frequencies


Select variable.

Click on Charts, another dialogue box will show up. Click Histogram in this dialogue box. Click on Continue.

Click on OK. The histogram will be displayed together with the frequency table.

Graphs Interactive Histogram This menu option allows user to define the interval and cutpoints.


Drag the variable into the domain target field.

Click on Options button to get into the options tab.

Under Scale Range choose the variable of the histogram (the same variable in the domain target field).

Uncheck Auto, this will allow you to enter Minimum (first cut point, that is, the lower bound of the first interval) and the Maximum (last cut point, that is, the upper bound of the last interval).

Click on Histogram button to get into the histogram tab.

Uncheck “Select interval size automatically”, then either enter your choice of number of intervals or enter your choice of interval width.

Click on OK.

With SPSS, data falling on a boundary are counted in the class below the boundary.

Example

Let’s make a histogram of the data we stored in the data file ads (created in Chapter 1). We’ll use the variable Ad_Count (in the first column). This column contains the number of ads per hour on prime time TV.

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Part IV: SPSS Guide 301

First we need to retrieve the data file. Use File Open Data. Scroll to the drive containing the worksheet. We used 3½ disk drive A. Click on the file.

The number of ads per hour of TV is in the first column under variable Ad_Count. Let us first use

Graphs Histogram. The dialogue box follows.

Select Ad_Count and enter it under Variable, as shown below.

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302 Technology Guide Understandable Statistics, 8th Edition

Click on OK. The following histogram with automatically selected classes will be displayed.

Now, let us draw a histogram for this data with four class intervals. Note that the low data value is 13 and the high value is 28. Using techniques shown in the text Understandable Statistics, we see that the class boundaries for 4 classes are 12.5; 16.5; 20.5; 24.5; 28.5. Use Graphs Interactive Histogram. The dialog boxes follows.



Now drag the variable Ad_Count into the domain target field as shown below.

Click on Options button to get into the options tab. Under Scale Range choose the variable ac (which is the label for Ad_Count). Uncheck Auto. Then enter 12.5 as Minimum and 28.5 as Maximum.



Now, click on Histogram button to get into the histogram tab. Uncheck “Select interval size automatically”, select Number of intervals, enter 4.

Click on OK. The histogram follows.



LAB ACTIVITIES FOR HISTOGRAMS

1. The ads data file contains a second column of data that records the number of minutes per hour consumed by ads during prime time TV. Retrieve the ads data file again and use the second column (under variable Min_Per_Hr) to

(a) make a histogram, letting the computer scale it. (b) sort the data and find the smallest data value. (c) make a histogram using the smallest data value as the starting value and an increment of 4 minutes.

Do this by setting the smallest value as the Minimum in the options tab and choosing 4 as the Width of interval in the histogram tab. You also need to choose an appropriate number as the Maximum in the options tab (Maximum = Minimum + Width*(number of intervals)).

2. As a project for her finance class, Linda gathered data about the number of cash requests made at an automatic teller machine located in the student center between the hours of 6 P.M. and 11 P.M. She recorded the data every day for four weeks. The data values follow.

25 17 33 47 22 32 18 21 12 26 43 25 19 27 26 29 39 12 19 27 10 15 21 20 34 24 17 18

(a) Enter the data. (b) Make a histogram for this data, letting the computer scale it. (c) Sort the data and identify the low and high values. Use the low value as the start value and an

increment of 10 to make another histogram.

3. Choose one of the following files from the CD-ROM.

Disney Stock Volume: Svls01.sav

Weights of Pro Football Players: Svls02.sav

Heights of Pro Basketball Players: Svls03.sav

Miles per Gallon Gasoline Consumption: Svls04.sav

Fasting Glucose Blood Tests: Svls05.sav

Number of Children in Rural Canadian Families: Svls06.sav

(a) Make a histogram, letting SPSS scale it. (b) Make a histogram using five classes.

4. Histograms are not effective displays for some data. Consider the data

1 2 3 6 7 4 7 9 8 4 12 10

1 9 1 12 12 11 13 4 6 206



Enter the data and make a histogram, letting SPSS do the scaling. Next scale the histogram with starting value 1 and increment 20. Where do most of the data values fall? Now drop the high value 206 from the data. Do you get more refined information from the histogram by eliminating the high and unusual data value?

STEM-AND-LEAF DISPLAYS (SECTION 2.3 OF UNDERSTANDABLE STATISTICS)

SPSS supports many of the exploratory data analysis methods. You can create a stem-and-leaf display with the following menu choices.

Analyze Descriptive Statistics Explore


Dependent List: Enter variables for making the display.

Display: Choose Plots under Display.

Then, click on the button Plots. Another dialog box will show up.

Select Stem-and –leaf. Click on Continue.

Click on OK.

Example

Let’s take the data in the data file Ads and make a stem-and-leaf display of Ad_Count. Recall that this variable contains the number of ads occurring in an hour of prime time TV.

Use the menu Analyze Descriptive Statistics Explore. In the dialog box, enter Ad_Count into the dependent list. Choose Plots under Display.



Now click on the button Plots. Another dialog box shows up. Select Stem-and-leaf.

Click on Continue. Then click on OK. The stem-and-leaf display follows.

The first column gives the depth of the data, that is, the number of data in this line. The second column gives the stem and the last gives the leaves. The display has 2 lines per stem. That means that leaves 0–4 are on one line and leaves 5–9 are on the next.



LAB ACTIVITIES FOR STEM-AND-LEAF DISPLAYS

1. Retrieve data file Ads again, and make a stem-and-leaf display of the data in the second column. This data gives the number of minutes of ads per hour during prime time TV programs.

2. In a physical fitness class students ran 1 mile on the first day of class. These are their times in minutes.

12 11 14 8 8 15 12 13 12 10 8 9 11 14 7 14 12 9 13 10 9 12 12 13 10 10 9 12 11 13 10 10 9 8 15 17

(a) Enter the data in a data sheet. (b) Make a stem-and-leaf display.


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CHAPTER 2 ORGANIZING DATA - Cengage