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Psychological Statistics Midterm
Descriptive Statistics - Techniques for summarizing the numeric properties of groups Inferential Statistics - The use of estimates to test hypotheses about parameters which cannot be measured directly Sample - Small group to represent the larger group of interest Population - The entire group of interest Estimates - Properties of samples Parameters - Properties of populations Nominal variables - Values are labels with no order (ex: faculty) Ordinal variables - Values are labels with order (ex: letter grades) Interval variables - Values are numbers with an arbitrary zero (ex: temperature)
Ratio variables - Values are numbers with a real zero (zero really means zero) (ex: age, height, etc.) Discrete information - limited number of values possible within the range of values Continuous information - all "in between" values are possible (ex: age, height, etc.) Cumulative frequency - sum of frequencies up to and including a given category Central location/Averages - A typical response (mean, median, mode) Variation - Spread of distribution - very spread out or condensed Sometimes around a measure of central location 4 measures of variation: range, mean deviation, variance, standard deviation Zero skew - Symmetric distribution Positive skew - many low values, few high values Negative skew - many high values, few low values
Median - A measure of central location that is the middle-ranked value Mode - Most frequently occuring value or the midpoint of the most frequently occuring interval Range - Measure of variation that is the difference between the two most extreme scores of the sample Does not improve with an increase in sample size Mean deviation - A measure of variation that is the mean of the absolute distance to the mean for a set of scores ∑ |Xi - mean| / N Variance - "s²" or "σ²" A measure of variation that approximates the average squared distance to the mean for a set of scores / Mean of the squared deviation scores s² = ∑(X - mean)² / (N-1) Standard deviation - "s" or "σ" A measure of variation that approximates the average distance of the mean for a set of scores. Square root of variance s = √s² Consistent estimate - An estimate (approximation to a parameter) that improves with increasing sample size
Biased estimate - An approximation for a parameter that contains systematic error so that it always over or under-estimates the parameter Standard score - "z" A transformation of a raw score into distance from the mean in units of standard deviation z = (X - mean) / s Causality - The assumption that a change in one variable directly brings about a change in another variable Correlation - "r" An indicator of bivariate linear relationship that gives the direction and strength of the relationship Covariance - An indicator of bivariate relationship that gives the direction of the relationship Coefficient of determination - "r²" Measures the proportion of the variation in one variable that can be accounted for by variation in another variable Dependent variable - The variable that is observed to assess the result of manipulating the independent variable Independent variable - The variable that is manipulated to study the effect on the dependent variable
The likelihood of either event A or event B both occuring Denoted as P(A or B) or P(A∪B) Permutations - The total number of orderings of a set or subset
