KEY TERMS
statistics descriptive statistics frequency distribution histogram frequency polygon skewed distribution symmetrical distribution measure of central tendency mode median mean measure of variability range standard deviation z score standard normal curve or standard normal distribution correlation correlation coefficient positive correlation negative correlation scatter diagram or scatter plot inferential statistics t test Type I error Type II error population sample | A subset of a population. A single number that presents information about the spread of scores in a distribution. 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. Erroneously concluding that study results are significant. A complete set of something— A branch of mathematics used by researchers to organize, summarize, and interpret data. Test used to establish whether the means of two groups are statistically different from each other. 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. A single number that presents some information about the “center” of a frequency distribution. A way of 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. An asymmetrical distribution; more scores occur on one side of the distribution than on the other. In a positively skewed distribution, most of the scores are low scores; in a negatively skewed distribution, most of the scores are high scores. A finding that two factors vary systematically in opposite directions, one increasing as the other decreases. Mathematical methods used to organize and summarize data. A finding that two factors vary systematically in the same direction, increasing or decreasing together. A number, expressed in standard deviation units, that shows a score’s deviation from the mean. The most frequently occurring score in a distribution. Mathematical methods used to determine how likely it is that a study’s outcome is due to chance and whether the outcome can be legitimately generalized to a larger population. 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. A graph that represents the relationship between two variables. The relationship between two variables. The score that divides a frequency distribution exactly in half so that the same number of scores lie on each side of it. A measure of variability; the highest score in a distribution minus the lowest score. A way of graphically representing a frequency distribution; a type of bar chart that uses vertical bars that touch. A symmetrical distribution forming a bell- Failing to find a significant effect that does, in fact, exist. A numerical indication of the magnitude and direction of the relationship (the correlation) between two variables. A distribution in which scores fall equally on both sides of the graph. The normal curve is an example of a symmetrical distribution. |