# Meaning of Important Terms in Psychology Part 1 for GRE

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Descriptive statistics: Mathematical tools used to describe and summarize numeric data.

Inferential statistics: Mathematical tools used for decision making, for generalizing from small samples, and for drawing conclusions.

Graphical statics: Techniques for presenting numbers pictorially, often by plotting them on a graph.

Frequency distribution: A table that divides an entire range of scores into a series of classes and then records the number of scores that fall into each class.

Histogram: A graph of a frequency distribution in which the number of scores falling in each class is represented by vertical bars.

Frequency polygon: A graph of a frequency distribution in which the number of scores falling in each class is represented by points on a line.

Central tendency: The tendency for a majority of scores to fall in the midrange of possible values.

Mean: A measure of central tendency calculated by adding a group of scores and then dividing by the total number of scores.

Median: A measure of central tendency found by arranging scores from the highest to the lowest and selecting the score that falls in the middle. That is, half the vales in a group of scores fall above the median and half fall below.

Mode: A measure of central tendency found by identifying the most frequently occurring score in a group of scores.

Variability: The tendency for a group of scores to differ in value. Measures of variability indicate the degree to which a group of scores differ from one another.

Range: The difference between the highest and lowest scores in a group of scores.

Standard deviation: An index of how much a typical score differs from the mean of a group of scores.

Z-score: A number that tells how many standard deviations above or below the mean a score is.

Normal curve: A bell-shaped distribution, with a large number of scores in the middle, tapering to very few extremely high and low scores.

Correlation: The existence of a consistent, systematic relationship between two events, measures, or variables.

Scatter diagram: A graph that plots the intersection of paired measures; that is, the points at which paired X and Y measures cross.

Positive relationship: A mathematical relationship in which increase in one measure are matched by increase in the other (or decreases correspond with decreases) .

Zero correlation: The absence of a (linear) mathematical relationship between two measures.

Negative relationship: A mathematical relationship in which increases in one measure are matched by decreases in the other.

Coefficient of correlation: A statistical index ranging from -1.00 to + 1.00 that indicates the direction and degree of correlation.

Perfect positive relationship: A mathematical relationship in which the correlation between two measures is + 1.00.

Perfect negative relationship: A mathematical relationship in which the correlation between two measures is -1.00.

Percent of variance: A portion of the total amount of variation in a group of scores.

Population: An entire group of animals, people, or object belonging to a particular category (for example, all college students or all married women) .

Sample: A smaller subpart of a population.

Representative sample: a small, randomly selected part of a larger population that accurately reflects characteristics of the whole population.

Random selection: Choosing a sample so that each member of the population has an equal chance of being included in the sample.

Statistical significance: The degree to which an event (such as the results of an experiment) is unlikely to have occurred by chance alone.

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