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# WGU RFC 1 ch 12

### Summary of Chapter 12

Formulas for statistical procedures are just basic mathematical procedures
first step toward analysis involves converting behavioral responses into some numeric system or categorical organization
Frequency refers to the number of times something occurs; with descriptive statistics
Nominal or ordinal variables frequency count by each value is very descriptive
frequency is more complicated for interval or ratio variables
Measures of central tendency indices that represent a typical score among a group of scores
mean arithmetic average of the scores, most frequently used measure of central tendency; appropriate for describing interval or ratio data
median midpoint in a distribution; 50% of the scores are above the median, and 50% are below the median; most useful when looking at ordinal variables or data sets in which the scores vary widely over distribution
mode score that is attained by more subjects than any other score (i.e., occurs most frequently); a set of course may have two or more modes; when nominal data are collected, the mode is the only appropriate measure of central tendency
two sets of data that are very different can have identical means or medians creating a need for measures of variability, indices that indicate how spread out a group of scores are
the range simply the difference between the highest and lowest score in a distribution and is determined by subtraction
quartile deviation one half of the difference between the upper quartile (75th percentile) and the lower quartile (25 percentile) in a distribution
quartile deviation more stable measure of variability than the rand and is appropriate whenever the median is appropriate
variance defined as the amount spread among scores, if the variance is small the scores are close together, if it is large, the scores are more spread out
standard deviation square root of the variance of a set of scores; it is the most stable measure of variability and takes into account every score
when plotted as a frequency graph a normal distribution forms a bell shape normal curve
when distribution is not normal it is said to be skewed, there are more extreme scores at one end than the other
negatively skewed the extreme scores are at the lower end of the distribution
positively skewed the extreme scores are at the upper or higher end of the distribution
percentile rank indicates the percentage of scores that fall at or below a given score
percentiles are appropriate for data measured on an ordinal scale
standard score reflects how many standard deviations a students score is above or below the mean
T score z score transformed to eliminate pluses or minuses
measures of relationship indicate the degree to which two sets of scores are related
degree of relationship expressed as a correlation coefficient, which is computed from two sets of scores from a single group of participants
Pearson r most appropriate measure of correlation when the sets of data to be correlated are expressed as either interval or ratio scales
Pearson r not valid if the relation between variables is not linear
Spearman rho appropriate measure of correlation when the variables are expressed as ranks
Created by: Xyrarose