Variability. Why is the study of variability important?. Allows us to distinguish between usual & unusual values In some situations, want more/less variability scores on standardized tests time bombs medicine. Measures of Variability. range (max-min) interquartile range (Q3-Q1)
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Allows us to distinguish between usual & unusual values
In some situations, want more/less variability
scores on standardized tests
interquartile range (Q3-Q1)
Lower case Greek letter sigma
Suppose that we have these data values:
Find the mean.
Find the deviations.
What is the sum of the deviations from the mean?
Square the deviations:
Find the average of the squared deviations:
The average of the deviations squared is called the variance.
Astandard deviation is a measure of the average deviation from the mean.
n deviations contain (n - 1) independent pieces of information about variability
An appliance repair shop charges a $30 service call to go to a home for a repair. It also charges $25 per hour for labor. From past history, the average length of repairs is 1 hour 15 minutes (1.25 hours) with standard deviation of 20 minutes (1/3 hour). Including the charge for the service call, what is the mean and standard deviation for the charges for labor?
If variables are independent
Bicycles arrive at a bike shop in boxes. Before they can be sold, they must be unpacked, assembled, and tuned (lubricated, adjusted, etc.). Based on past experience, the times for each setup phase are independent with the following means & standard deviations (in minutes). What are the mean and standard deviation for the total bicycle setup times?