Statistics: the use of mathematics to organize, summarize, & interpret numerical data. Frequency distribution: an orderly arrangement of scores indicating the frequency of each score or group of scores (tally) histogram: a bar graph that presents data from a frequency distribution. Frequency polygon: a line figure used to present data from a frequency distribution. descriptive statistics: used to organize & summarize data. negatively skewed distribution: most scores pile up at the high end of the scale. positively skewed distribution: scores pile up at the low end of the scale. a few extreme scores at one end pull the mean, & slightly the median, away from the mode. mean may be misleading & the median usually provides the most accurate central tendency. standard deviation: an index of the amount of variability in a set of data. steps of calculating the standard of deviation 1.