Data Analysis and
Presentation
Describing and Presenting
Data
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Three important criteria—accuracy,
conciseness, and understandability
Researchers should always present their
data in ways that most accurately represent
the data
Numerical data can be classified as
numerical (example: percentages, (means)
or graphical (graphs) method)
Statistics
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Three areas:
1) Descriptive – central tendency,
dispersion measures
2) Relational – univariate, bivariate, or
multivariate statistics
3) Inferential – difference of means,
statistical significance tests
Measures of Central
Tendency
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The mean—average; most common and
useful measure of central tendency;
impacted by extreme scores
The median—middle score of a
distribution; less affected by extreme
scores (“outliers”)
The mode—most frequent score
Measures of Variability
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Measures of Variability—descriptive statistics that
convey information about the spread or variability
of a set of data
Variance—a numerical index of the variability in a
set of data
Standard deviation—a measure of variability that
is equal to the square root of the variance
Range—the difference between the highest and
lowest scores in a distribution
Relational Statistics
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1) univariate – study of one variable for a
subpopulation (ex: age of murderers)
2) bivariate – study of relationship between
two variables (ex: correlation)
3) multivariate – study of relationship
between three or more variables (ex:
multiple correlation)
Correlation
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Measure of the strength of some
relationship between two variables, but not
causality.
Correlations can be positive, negative, or
zero.
Strength of relationship depends on
coefficient.
Correlations
Correlation
Strength
0.8 to 1.0
Very strong
0.6 to 0.8
Strong
0.4 to 0.6
Moderate
0.2 to 0.4
Weak
0.0 to 0.2
Very weak
Inferential Tests
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Refer to a variety of tests for inferential
purposes.
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1. difference of means – to test hypotheses,
most common is Z-test.
2) statistical significance – most common are ttest and chi-square (used for less than interval
data)
Frequency Distributions
A table that summarizes raw data by
showing the number of scores that fall within
each of the categories
Pounds Lost by Dieter
Frequency
0
5
1-5
10
6-10
15
Over 10
5
Frequency Histograms and
Polygons
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Sometimes information in frequency
distributions is more easily grasped when it is
presented graphically
Histogram is used when horizontal (x-axis)
variable is measured on an interval or ratio
scale (bars on graph touch each other)
If data is nominal or ordinal, the bars do not
touch each other and it is a bar graph
Graphical Methods of Reporting
Data
30
25
20
0 pounds
1-5 pounds
6-10 pounds
15
10
5
0
men
women