Lecture 6: Computing The Standard Deviation

Question 1

What statistics measure central tendency?

Answer 1

MEAN MEDIAN AND MODE

Question 2

What statistics measure dispersion/variability?

Answer 2

RANGE AND STANDARD DEVIATION!

Question 3

Why is the standard deviation usually more useful than the range? (3 reasons!)

Answer 3

• Range is only based on 2 values so no sense of the typical values —> SD gives sense of typical!
• Can see relevant scores compared to rest of sample
• Range is affected by ANOMALIES especially for larger samples

Question 4

How do you compute the sample standard deviations?

Answer 4

1) Compute mean
2) Compute difference between each value and mean
3) Square the differences
4) Sum all square differences
5) Divide that sum by one less than sample size
6) Square root the result!

Question 5

Why divide by one less than the number of values instead of by the number of values?

Answer 5

1. Extreme samples are unlikely to be represented —> understates true variability
2. Smaller the sample the more it’s needed