Measures of Variability Learning to calculate the Standard

Measures of Variability Learning to calculate the Standard Deviations

Measures of Variability n Using the Deviation formula to calculate the Standard Deviation. u These formulas define what a standard deviation is but are cumbersome to calculate from.

Measures of Variability

Measures of Variability n Using the Deviation formula to calculate the Standard Deviation. u We can also calculate the SD using the deviation formula when we have grouped data.

Measures of Variability

Measures of Variability n Calculator Formula u The formula you will almost always use to calculate the SD is the calculator formula.

Measures of Variability

Measures of Variability n Computing the Standard Deviation from Grouped data u Need to correct for error due to grouping. u Sheppard’s correction for grouping F SD not the same, even with symmetrical distributions. F If there as many as 12 -15 class intervals, the correction really makes little difference.

Measures of Variability n Summary of Standard Deviation u u u S. D. is the most used and most important measure of dispersion. Related to Variance. Arithmetic operations can be performed with it Most stable measure of dispersion. 68% of the scores fall ± 1 S. D. u 99. 74% of the scores fall ± 3 S. D. u 95. 4% of the scores fall ± 2

Measures of Variability n Relationships among measures of dispersion

Measures of Variability n Next: u Measures of Skewness u Measures of Kurtosis u Standard Scores and other neat stuff