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Readings
• Chapter 2 Measuring and Describing Variables (Pollock) (pp.32-33)
• Chapter 2 Descriptive Statistics (Pollock Workbook)
• Homework: Chapter 1 Introduction to SPSS (Pollock Workbook) – Question 1 Parts A &B – Question 2
About the Homework
• It must be turned in during class.
• It cannot be emailed
• It must appear on the workbook paper (original or a photocopy)
• You cannot:
Course Learning Objectives
• Students will learn the research methods commonly used in behavioral sciences and will be able to interpret and explain empirical data.
• Students will achieve competency in conducting statistical data analysis using the SPSS software program.
What about them
• The values matter
• Your variable includes all possible values, not just the one’s that you assign.
• Name, order, and the distances between values matter.
Interval Level Variables
• The values matter at this level
• The distances matter
• The zero is arbitrary
Ratio Variables
• The Full properties of numbers
• A zero means the absence of a property
• Classify, order, set units of distance
Descriptive Statistics
• These simply describe the attributes of a single variable.
• You cannot test here (you need two variables)
• Why do them?
Categories of Descriptive Statistics
Measures of Central Tendency• The most common, the
middle, the average
• Mean, Median and Mode
Measures of Dispersion• How wide is our range of
data, how close to the middle are the values distributed
• Range, Variance, Standard Deviation
Frequency Distributions• This Provides counts and percentages (relative
frequencies) of the values for a given variable
• Computing a relative Frequency
• The Cumulative Percent is percentage of observations less than or equal to the category
Examples
• St. Edward’s Data
The Mode
• the most frequent observation of the variable in a distribution
• Which category is most common
• There can be more than 1
Examples
• What are the Modes here?
1. 110,105.100.100.100.100.99.982. 110.105.105.105.100.95.95.95.90
The Median
• It only tells us one thing
• the value that lies in the middle of the data when arranged in ascending order.
Examples
• The University of Texas
• The 78704 Zip Code
Examples
• The middle observation = (N+1)/2
• Characteristics and problems of the median
• Three Examples – (133,113,112,95,94) – (27,12,78,104,45,34) – (105,102,101,92,91,80)
Finding the Median
• location of median case (1747+1)/2 = 874 • Where Does that case fall?
– Case 1 through 534 = has value of 0 – Case 535 through 1747 = has value of 1
• Case 874 is more than 535 and less than 1747 • THE MEDIAN IS 1, the category is voted
You can also look here for where 50% falls
About the Mean
• Characteristics of the Mean
• Problems of the Mean
An Example
Name Income
Skipper 50.00
Gilligan 150.00
Mary Ann 150.00
Professor 400.00
Mrs. Howell 500.00
Mr. Howell 1000.00
Ginger 3000.00