POPULATION BASED CALCULATION

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CONFIDENCE LEVE

Confidence Level & Value for Z

C.I = 90% , Z = 1.645C.I = 95% , Z= 1.960C.I= 99% , Z= 2.575C.I= 99.9%, Z= 3.29

Calculating Sample Size w.r.t Population

The Manual Calculation MethodTo perform sample size calculation manually, you need

the following values:

Population Value: Size of the population from which the sample will be selectedExpected Frequency “P” of the Factor under Study always err toward 50%

Worst Acceptable Frequency (ALPHA,D)If 50% is the true rate in the population, what is the result farthest from the rate that you would accept in your sample? If your confidence interval were 4%, then your worst acceptable frequency would be 54% or 46%.

FORMULA

k = (Z * Z) [P (1-P)/(D*D)]

Sample Size = k/ [1 + (/population)]

P = True proportion of factor in the population, or the expected frequency value.

D = Maximum difference between the sample mean and the population mean,Or Expected Frequency Value minus (-) Worst Acceptable Value

EFV = 50 % and Worst Acceptable Value= 45- 55%, D= 5%

Z = Area under normal curve corresponding to the desired confidence level

CalculationWith confidence Interval C.I = 95 % & Z=1.96Assuming that 50% of working women focus on

ready to cook food then P=0.5, Margin of Error = D = 5 %Assuming Population, N = 2800

k = (Z * Z) [P (1-P)/(D*D)]K= (1.96)(1.96)[0.5(1-0.5)/(0.05)(0.05)] = 384.16

Sample Size = k/[1+(k/population) = 384.16/[1+(384.16/2800)] =338 Sample

Sample Size Table

Table :Sample Values are calculated at 50 % Expected Frequency “P” .

Example In the Al Haouz project, it has been estimated that roughly 30%

(0.3) of the children in the project area suffer from chronic malnutrition. This figure has been taken from national statistics on malnutrition in rural areas. Use of the standard values listed above provides the following calculation.

Calculation:

k= 1.96² x .3(1-.3) = 322 .05²

SAMPLE SIZE = 323 [ 1 +( 323 / 2800) ] = 361

Reference

http://bphc.hrsa.gov/policiesregulations/performancemeasures/patientsurvey/calculating.html

http://www.raosoft.com/samplesize.html