Variance and Standard Deviation

• Greater understanding = provides summary of a population dispersion
• Variance = arithmetic mean of the squared deviations from the mean
• Standard deviation = the square root of the variance
• Only zero = if all observations are the same
• Values near the mean = variance and standard deviation will be small
• Values are dispersed from the mean = variance and standard deviation will be large
• Variance overcomes the weakness of the range = using all population values
• Step 1 = find the mean
• Step 2 = find the difference between each observation and the mean; square that difference
• Step 3 = sum all squared differences found in step 2
• Step 4 = divide the sum of the squared differences by the number of items in a population
• The larger the variance = the greater the dispersion of data