Outline

Finish discussion of  Variance and Standard Deviation

Discuss Applications of measures of spread

Discuss Properties of SD

MEASURES OF SPREAD: APPLICATIONS

·        Range and SD are sensitive to extreme scores.  In such cases the semi-interquartile range is best.

·        When your distribution of scores is skewed, the SD does not provide a good index of spread.

·         With a skewed distribution, use the semi-interquartile range

PROPERTIES OF SD

·        Adding a constant to each score (or subtracting a constant) will not change SD, but will change the mean, by an amount equal to the constant.

·        Multiplying each score by a constant will cause the SD to be multiplied by the same constant (as well as the mean).  Dividing each score by a constant will cause the SD to be divided by the same constant (as well as the mean).