A Statistics Refresher
What are Scales of Measurement?
• Nominal
– Categories
• Ordinal
– Magnitude
• Interval
– Magnitude and equal interval
• Ratio
– All others and has a true zero point
Examples
• Groups of low, medium, high?
• How much you like something?
– 1 not at all 5 very much
Frequency Distribution
• Summary information of scores and their occurrence.
Grouped Frequency Distribution
• Intervals replace specific values
– Identification of 12-15 class intervals recommended
Example of G.F.D.
• 20 students surveyed.
– Values are the number of alcoholic beverages.
– How do you create a frequency distribution using six classes?
Steps
• Step 1: Find the highest and lowest values: H = 9 and L = 0.
• Step 2: Find the range:
R = H – L = 9 – 0 = 9.
• Step 3: Select the number of classes desired. In this case: 6.
• Step 4: Find the class width by dividing the range by the number of classes. Width = 9/6 =
1.5. Value is rounded up.
• Step 5: Select a starting point for the lowest class limit: 0, 2, 4, 6, 8, 10.
• Step 6: Upper class limits will be 1, 3, 5, 7, 9, and 11.
Most Common Graphs
• Histogram
• Frequency Polygon
• Ogive
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