5. Typical Sample Sizes

7. Incidence Rate Calculation

8. Sample Size Variance (standard deviation) Magnitude of error Confidence level

9. Sample Size Formula

10. Sample Size Formula - Example Suppose a survey researcher, studying expenditures on lipstick, wishes to have a 95 percent confident level (Z) and a range of error (E) of less than $2.00. The estimate of the standard deviation is $29.00.

11. Sample Size Formula - Example

12. Suppose, in the same example as the one before, the range of error (E) is acceptable at $4.00, sample size is reduced. Sample Size Formula - Example

14. 99% Confidence Calculating Sample Size  1389  265.37 2  2 53.74 2        2 )29)(57.2( n 2         347   6325.18 2  4 53.74 2        4 )29)(57.2( n 2       

15. Standard Error of the Proportion

16. Confidence Interval for a Proportion

17. Sample Size for a Proportion

18. 2 2 E pqz n  Where: n = Number of items in samples Z 2 = The square of the confidence interval in standard error units. p = Estimated proportion of success q = (1-p) or estimated the proportion of failures E 2 = The square of the maximum allowance for error between the true proportion and sample proportion or zs p squared.

19. Calculating Sample Size at the 95% Confidence Level 753  001225. 922.  001225 )24)(.8416.3(  )035(. )4 )(. 6(.) 96 1. ( n 4.q 6.p 2 2   