Random Sampling -Cont. - mo3270102

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Estimated minimum monthly population = 456
Estimated maximum population = 732
The sample size from the table of sampling sizes for normal sampling
levels in Appendix F, Table 1, is 147. This is the sample size for the
minimum population of 456 and the number of additional samples
required for the population in excess of the minimum and up to the
maximum population must now be calculated.
The sampling rate = 147/456 = 32.2%
Additional number Of samples required = .322(732-456) = 89
Thus147 + 89 or a total of 236 samples, must be selected from the
population.
When the duration of the contract is less than 12 months, it is possible for
the sample size using minimum sampling level to be greater than the sample
size using the normal sampling level.  If this occurs, the sample size must
be adjusted.  This adjustment need only be carried out when the contract
duration is less than 12 months.
The RSED computer program available from on the EFDs makes the necessary
adjustments automatically, and a manual calculation is rarely necessary.
The manual calculations shown below are included to demonstrate the
principles involved.
Example:  The following example determines sample size for services
received over a three month period. A comparison is made between the sample
size determined using the normal sampling level tables in Appendix F, Table
1, and the sample size using the minimum sampling level in Appendix F, Table
2, as follows:
MINIMUM
NORMAL
LEVEL
LEVEL
(Table 2)
Population (Table 1)
Month
-
159
1
600
-
166
2
700
-
159
3
600
Total
560
1900
484
The minimum sample size is greater, and it therefore becomes necessary
to prorate the Table 2 sample size for each month according to the Table1
sample sizes, rounding fractional amounts up to the next higher whole
number.
85