Measures of Variability

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Presentation transcript:

Measures of Variability Learning to calculate the Standard Deviations

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

Measures of Variability

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

Measures of Variability

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

Measures of Variability

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

Measures of Variability Summary of Standard Deviation 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. 95.4% of the scores fall ±2 S.D. 99.74% of the scores fall ±3 S.D.

Measures of Variability Relationships among measures of dispersion

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