Hello R.gate community
If there are obstacles in determining the size of target population, how can we calculate the appropriate sample size in this case?
Regards
If key-variable of the population is quantitative, use n=Z2*s2/d2. Where: n - this is what are looking for (minimum sample size), Z - is the value of the distribution function ( alpha equals to 0,05), s - is the population standard deviation, and d - is acceptable standard error of the mean (it is up to you). Of course, you don't know the population (typical in tourism studies). So, I suggest to estimate s using results from pilot research. After the pilot research calculate s=s'*(n'/(n'-1))^0,5. Where: n' - is the sample size of pilot research, and s' - is the the standard deviation of sample of pilot research.
For qualitative study , Where the population is unknown, the sample size can be derived by computing the minimum sample size required for accuracy in estimating proportions by considering the standard normal deviation set at 95% confidence level (1.96), percentage picking a choice or response (50% = 0.5) and error of margin d=0.05. Applying n = z 2 (p)(1-p)/d2. It will be around 384
Hicham Beroual , not all formulas require you to know the size N of the population, i.e. you do not need to always have N to calculate the sample size. Let's say you want the sample size (n) to estimate a proportion (p), given the inverse of the normal cumulative distribution (z) associated to a confidence interval, and an error (e), then:
n = (1/e^2)*((z^2)*(1-p)*p)
For more details see for example:
Code Sample size calculators
Hicham Beroual , updating my answer above, I have created a sample size calculator in Excel, with and without information of the population size:
Method Sample size calculator in Excel (for a proportion)
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