Normality of Distribution

frequency table

method or organizing data by listing every possible value in first column of numbers and frequency of each value as second column

skewness

mean, median, and mode not equal

interferes with validity of many statistical analyses

positively skewed

largest portion of data is below mean

mean>median>mode

negatively skewed

largest portion of data is above the means

mean<median<mode

kurtosis

degree of peakedness of frequency

extreme kurtosis can affect validity of statistical analysis because scores have little variance

mesokurtic

kurtosis score of zero

leptokurtic

kurtosis value above zero

platykurtic

kurtosis value below zero that are negative

Shapiro-Wilk’s W test

formal test of normality that assesses whether a variable’s distribution is skewed and/or kurtotic

has ability to calculate both skewness and kurtosis by comparing shape of variables frequency distribution to that of a perfect normal curve