For sample size calculation of unknown population size, you can use the following formula: n= z2. [p*q]/d2), which is used to calculate the sample size of a qualitative variable in prevalence or cross-sectional studies. In this formula, n is the sample size, P is the estimated proportion of the study variable or construct based on previous studies or pilot studies (70%), q = 1-P (30%), and d is the margin of error (5%). z is the Z-score or a standard normal deviate corresponding to (100%, α/2%), where α refers to the significance level or the probability of making a type I error. The z score for different significance levels is: 1.96 for 5%, 1.28 for 10%, and 2.58 for 1%. I have added some hypothetical values and the sample size would be 323.
You can refer to any epidemiological textbook or the following reference for details.
Charan J, Biswas T (2013) How to calculate sample size for different study designs in medical research? Indian Journal of Psychological Medicine. 35, 2, 121-126.
Hi Devisri,
Sample size depends on many factors including but not limited to:-
1. The hypothesis you are testing (e.g. single population mean, proportions, two population means ...)
2. The sampling procedure (e.g. simple random, stratified, cluster...)
3. The nature of the population (homogeneous, heterogeneous,...)
4. Available resources and
5. The seriousness of making type one error.
I don't know what you mean by "Unknown" here. Perhaps you shed more light.
For sample size calculation of unknown population size, you can use the following formula: n= z2. [p*q]/d2), which is used to calculate the sample size of a qualitative variable in prevalence or cross-sectional studies. In this formula, n is the sample size, P is the estimated proportion of the study variable or construct based on previous studies or pilot studies (70%), q = 1-P (30%), and d is the margin of error (5%). z is the Z-score or a standard normal deviate corresponding to (100%, α/2%), where α refers to the significance level or the probability of making a type I error. The z score for different significance levels is: 1.96 for 5%, 1.28 for 10%, and 2.58 for 1%. I have added some hypothetical values and the sample size would be 323.
You can refer to any epidemiological textbook or the following reference for details.
Charan J, Biswas T (2013) How to calculate sample size for different study designs in medical research? Indian Journal of Psychological Medicine. 35, 2, 121-126.
Devisri Subramaniam, I assume that unknown may for example be a population of a city like Delhi. Two to three years after the census, the population can only be an approximate. Meaning that it is unknown. Use the Krejcie and Morgan sample size table.
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