How to decide population and sample size,if working on four sectors in Delhi NCR?How to get population details as sectors are too vast?Than how to freeze population size?For example,How many employees are working in banking sector in DELHI NCR?
There are certain ways. If you have sample framework. It will make things bit easier. To attain sample framework. You have to check the registered 'organisations/etc' official list from the sector. In case of banking sector, you can attain the list from the Government authorities. Thus, you can split the sample into regions. Since, I believe that 70% of the banking sector in India is state-owned thus the best bet will will seeking list of banks in a region via Google, of Government office does not accommodate you.
Coming to the determination of the sample size. If your study is largely quantitative then, Roscoe (1975) argued that above 30 and below 500 could be the representative population. Furthermore, you can use the Marginal Error formula to determine the sample size, only if you know the sample framework. If you do not know sample size or even the population than remember a sample size of 200-400 is enough to draw logical conclusion because higher then number of responses go then lower will be the sig value, irrespective of the relationship.
In case, you are commencing qualitative study, you shall focus on "point of saturation". According to Morse (2010), anything between 30 to 50 responses are sufficient to reach point of saturation.