Transcript Appendix A: Statistics

Appendix A
Descriptive Statistics
Statistics used to organize and summarize data
in a meaningful way
Frequency Distributions
A summary of how often various scores occur
in a sample of scores. Score values are
arranged in order of magnitude, and the
number of times each score occurs is
recorded
Histogram
A way of graphically representing a frequency
distribution; a type of bar chart that uses
vertical bars that touch
Frequency polygon
a way a graphically representing a frequency
distribution; frequency is marked above
each score category on the graph’s
horizontal axis, and the marks are connected
by straight lines
Skewed Distributions
An asymmetrical distribution; more scores
occur on one side than the other; In a
positively skewed distribution, more scores
are low
Symmetrical Distribution
A distribution in which the scores fall equally
on both sides of the graph, the normal curve
is an example
Measure of Central Tendency
A single number that presents some
information about the “center” of a
frequency distribution
Mode
The most frequent occurring score in a
distribution
Median
The score that divides a frequency in half, so
that the same number of scores lie one both
sides
Mean
The sum of a set of scores in a distribution
divided by the number of scores; the mean
is usually the most representative measure
of central tendency
Measure of Variability
A single number that presents information
about the spread of scores in a distribution
Range
A measure of variability; the highest score
distribution minus the lowest score
Standard Deviation
A measure of variability; expressed as the
square root of the sum of the squared
deviations around the mean divided by the
number of scores in the distribution
z Score
A number, expressed in standard deviation
units, that shows a score’s deviation from
the mean
Standard Normal Curve
A symmetrical distribution forming a bellshaped curve in which the mean, median,
and mode are all equal and fall in the exact
middle
Correlation
The relationship between two variables
Correlation Coefficient
A measure of the magnitudes and directions of
the relationships between two variables. The
closer the correlation is to +1 or –1, the
stronger the relationship is. A positive
correlation coefficient indicates that as one
variable increase, the other tends to
increase, the negative correlation coefficient
indicates as one variable increases, the other
tends to decrease
Scatter Diagram
A graph that represents the relationship
between two variables
Inferential Statistics
Statistical techniques that allow researchers to
determine whether the outcomes in a study
are likely to be more than just chance events
and whether they can legitimately
generalized to a larger population
Population
A complete set of something-people,
nonhuman animals, objects, or events
Sample
A subset of a population