Reliability—consistency or repeatability of results.Validity—the extent to which an instrument measures or predicts what it is supposed to
measure or predict.Statistics—a field that involves the analysis of numerical data about representative
samples of populations.Descriptive statistics—numbers that summarize a set of research data obtained from a
sample. Key concepts of descriptive statistics include:- Frequency distribution—an orderly arrangement of scores indicating the frequency
of each score or group of scores. - Central tendency—average or most typical scores of a set of research data or distribution.
mode—most frequently occurring score in a set of research data (“quick and dirty”).
median—the middle score when a set of data is ordered by size.
mean—the arithmetic average of a set of scores. - Variability—the spread or dispersion of a set of research data or distribution.
Range—the difference between the largest score and the smallest score (“quick and
dirty”). - Standard deviation (SD)—measures the average difference between each score and
the mean of the data set. - Normal distribution—bell-shaped curve that represents data about how lots of
human characteristics are dispersed in the population. - Percentile score—the percentage of scores at or below a particular score (from 1
to 99). - Correlation coefficient (r)—a statistical measure of the degree of relatedness or asso-
ciation between two sets of data that ranges from -1 to +1.
Inferential statistics—statistics that are used to interpret data and draw conclusions.Statistical significance (p)—the condition that exists when the probability that the
observed findings are due to chance is less than 1 in 20 (p<.05) according to some psy-
chologists, or less than 1 in 100 (p<.01) according to those with more stringent stan-
dards.Ethical guidelines—suggested rules for acting responsibly and morally when conduct-
ing research or in clinical practice.64 STEP 4. Review the Knowledge You Need to Score High
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