Abridged Cozby's slides for RM

1. UNDERSTANDING RESEARCH
RESULTS: DESCRIPTION AND
CORRELATION
© 2012 The McGraw-Hill Companies, Inc.

2.  Nominal
 No numerical, quantitative properties
 Levels represent different categories or groups
 Ordinal
 Order the levels from lowest to highest
 Interval
 Intervals between levels are equal in size
 Can be summarized using means
 No absolute zero
 Ratio
 Equal intervals
 Absolute zero
 Can be summarized using mean
© 2012 The McGraw-Hill Companies, Inc.

3.  Three basic ways to describe results:
 Comparing Group Percentage
 Correlating Individual Scores
 Comparing Group Means
© 2012 The McGraw-Hill Companies, Inc.

4.  Graphing Frequency Distributions
 Pie charts
 Bar graphs
 Frequency polygons
 Histograms
© 2012 The McGraw-Hill Companies, Inc.

5. © 2012 The McGraw-Hill Companies, Inc.

6. © 2012 The McGraw-Hill Companies, Inc.

7. © 2012 The McGraw-Hill Companies, Inc.

8.  Central Tendency
 Mean
 Found by adding all the scores and dividing by the number of
scores
 Indicates central tendency with interval or ratio scales
 Median (Mdn)
 The middlemost score, or score that divides the group in half (with
50% scoring below and 50% scoring above the median)
 Indicates central tendency with ordinal, interval, and ratio scales
 Mode
 Most frequently occurring score
 Indicates central tendency with all scales including nominal scales
© 2012 The McGraw-Hill Companies, Inc.

9. © 2012 The McGraw-Hill Companies, Inc.

10.  Variability – the amount of spread in the
distribution of scores
 Standard deviation = (s) (SD) in reports
 Range
 Difference between highest and lowest score
 Variance (s²)
 Square of the standard deviation
© 2012 The McGraw-Hill Companies, Inc.

11. y-axisorordinate
x-axis or abscissa
© 2012 The McGraw-Hill Companies, Inc.

12.  Pearson r: the Correlation Coefficient
 Pearson’s r indicates:
 Strength of relationship
 Direction of relationship
 Values of r range from 0.00 to ±1.00
 Can be described visually using scatterplots
© 2012 The McGraw-Hill Companies, Inc.

13. © 2012 The McGraw-Hill Companies, Inc.

14. © 2012 The McGraw-Hill Companies, Inc.

15.  Restriction of Range
 Curvilinear Relationship
© 2012 The McGraw-Hill Companies, Inc.

16.  Refers to the strength of association between
variables
 Pearson r is one indicator of effect size
 Advantage of reporting effect size is that it
provides a scale of values that is consistent
across all types of studies
© 2012 The McGraw-Hill Companies, Inc.

17.  Differences in effect sizes
 Small effects near r = .15
 Medium effects near r = .30
 Large effects above r = .40
 Squared value of the coefficient r² - transforms
the value of r to a percentage
 Percent of shared variance between the two
variables
© 2012 The McGraw-Hill Companies, Inc.

18.  Infers whether the results will hold up if the
experiment is repeated several times, each time
with a new sample of research participants
 Inferential Statistics
© 2012 The McGraw-Hill Companies, Inc.