More complex sampling strategies (cont.)

Exercise

In a district stratified geographically into urban and rural areas, a proportionally stratified sample of 2500 individuals was taken to estimate the unmet need for family planning. The table below shows the populations of the two areas and the number of individuals with unmet need sampled from each of the two strata.

interaction Complete the table as follows:

Then calculate (to 2 decimal places where relevant):

Area Population Sample Size Number with unmet need in sample Percentage of the sample with unmet need Estimated total with unmet need
Urban 1,200,000 283
Rural 400,000 210
Total 1,600,000 2500 493

Hint: Rounding will affect your results and should only be done at the presentation stage and not during calculations.

This table shows the calculations used to obtain the correct values (given in bold).

Area Population Sample Size Number with unmet need in sample Percentage of the sample with unmet need Estimated total with unmet need

Urban

1,200,000

(1,200,000/1600000)
*2500 = 1875

283

(283/1875)
*100 = 15.09333333333333. Rounded to 15.09.

1,200,000
*0.1509333333333333 =
181120

Rural

400,000

(400,000/1,600,000)
*2500 = 625

210

(210/625)
*100 = 33.60.

400,000
*0.3360 = 134400

Total

1,600,000

2500

493

(493/2500)
*100 = 19.72

181,120
+ 134,400 = 315520
Alternatively;
1,600,000
*0.1972 = 315520

Note that you can calculate the estimated total with unmet need in two ways, firstly by summing the estimated total in each stratum, and secondly by multiplying the proportion of the sample with unmet need by the total population. The two results should always agree if proportional stratified sampling has been used.

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