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 bell- shaped 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