Chapter 2 Presenting Data in Charts and Tables. Why use charts and graphs? Visually present information that can’t easily be read from a data table. Many details can be shown in a small area.
Why use charts and graphs?
Computer software can be used to create charts and graphs:
How to present categorical data?
Bar chart example:
Pie char example:
How to present numerical data?
The ordered array
The sequence of data in rank order:
(min to max)
Tabulating Numerical Data:
Why use a Frequency Distribution?
Organizing data set into a table of frequency distribution:
The number of classes can be determined by using the formula: 2k>n
-k is the number of classes
-n is the number of data points
Prices of laptops sold last month at PSC:
299, 336, 450, 480, 520, 570, 650, 680, 720
765, 800, 850, 900, 920, 990, 1050, 1300, 1500
In this example, the number of data points is n=18.
If we try k=4 which means we would use 4 classes, then 24=16 that is less than 18. So the recommended number of classes is 5.
-The class interval should be the same for all classes
-Class boundaries never overlap
-The class interval can be expressed in a formula:
Where i is the class interval, H is the highest value in the data set, L is the lowest value in the data set, and k is the number of classes.
In the example above, H is 1500 and L is 299. So the class
interval can be at least =240.2. The class
interval used in this data set is 250
260 up to 510
510 up to 760
760 up to 1010
1010 up to 1260
1260 up to 1510
(midpoint=(Lower bound+ Upper bound)/2)
Laptop selling Frequency Cumulative Freq.
260 up to 510 44
510 up to 76059
760 up to 1010615
1010 up to 1260116
1260 up to 1510218
Example of histogram:
How can you construct the histogram in SPSS?
How can you construct the polygon in SPSS?
Ogive—a graph of cumulative frequency
How can you construct the Ogive in SPSS?
2. The following stem-and-leaf chart shows the number of units produced per day in a factory.
3. The following frequency distribution represents the number of days during a year that employees at GDNT were absent from work due to illness.
Number of Number of
0 up to 45
4 up to 810
8 up to 126
12 up to 168
16 up to 202