Instructor Resource
Treadwell and Davis, Introducing Communication Research: Paths of Inquiry, 4e
SAGE Publishing, 2020
Lecture Notes
Chapter 7: Summarizing Research Results: Data Reduction and Descriptive
Statistics
Learning Objectives
7-1 Describe the concept of descriptive statistics and provide examples.
7-2 Describe the concept of data reduction and provide examples.
Chapter Summary
This chapter begins by describing the concept of descriptive statistics. Next, the chapter
describes the concept of data reduction. Finally, the chapter explains and calculate the following
Annotated Chapter Outline
I. Introduction
A. Reducing data to comprehensible term
1. Tables summarize the data and relationships within the data
II. Preliminary Considerations: Missing Data and Anomalous Data
A. Missing data
1. The first step in data analysis is to decide what data to use
Instructor Resource
Treadwell and Davis, Introducing Communication Research: Paths of Inquiry, 4e
SAGE Publishing, 2020
B. Anomalous data
1. Data that appears “out of line.”
2. Discrepancies may also indicate that measurement tools need closer examination.
III. Data Reduction
A. Data reduction and univariate data
1. Univariate data is looking at each variable on its own.
B. Data reduction and bivariate data
1. Researchers are interested in how variables relate.
2. “Two by two” summary tables that summarizes the relationship between variables
6. Any table can be rotated.
C. Data reduction and multivariate data
1. Multivariate analysis studies the interaction of three or more variables.
IV. Measures of Central Tendency: Mean, Median, and Mode
A. Mean
1. Mean is often called the average value.
B. Mode
1. Mode is the most frequent value.
Instructor Resource
Treadwell and Davis, Introducing Communication Research: Paths of Inquiry, 4e
SAGE Publishing, 2020
C. Median
1. Median is the middle range value.
D. Distribution
1. Three modes are a tri-modal distribution.
V. Measures of Dispersion: Minimum, Maximum, Range, Interquartile Range,
Variance, and Standard Deviation
A. Minimum, maximum, range, and interquartile range
1. Minimum—the lowest value in a range.
B. Variance and standard deviation
1. Variance—a measure of the extent to which values in a data set vary.
a. Subtract the mean value for the group from each individual value.
2. Standard deviation is the square root of the variance.
VI. Z Score
A. Compute a z score
1. Once we have computed a group’s standard deviation for a variable, we can
compute a z score for any individual in the group.
Instructor Resource
Treadwell and Davis, Introducing Communication Research: Paths of Inquiry, 4e
SAGE Publishing, 2020
3. Questions use different metrics (units of measurement) and are of a different
VII. The Chi-Square Test
A. Essential labels
1. Cannot calculate nominal labels.
B. Chi-square: formula
1. Need to know the degrees of freedom (df).
Commented [TW2]: Add to PP