how to get my sample size

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    i am doing a survey on a luxury perfume shop in ¨PAris and i need to know how to find my sample size of clients to survey
    i have already designed my questionnaire but how many people should i interview and how to find it correctly
    many thanks



    Hello Janeessa,
    I have read somewhere that with this kind of surveys, if you have 1,600 sample size (consider that all 1,600 replied to your survey), you have a + 2.5 % margin of error.  I’m not sure though if others would agree with these, but I think I read this in a statistics website (maybe here), I just forgot the url.


    Van Loon

    You should take a look of how big the market is, i.e., how many people in Paris are in the group that could consum the product. If it is a parfum that is very expensive, your target group should be the people that have a lot of money. Next step is to ask how many people in Paris (women) have a lot of money. Most of the time the government has a census saying how many people are in each group of income.
    An then you can define the size of your sample by using Minitab.


    Robert Butler

      Jan is pointing you in the right direction.  You will have to investigate the issues of stratified random sampling in order to determine your sample size.  With an expensive perfume, you will need to stratify on such things as income, disposable income spent on luxury items, age, ethnic background, religious background, etc.  If you don’t stratify you will wind up with survey results that will tell you the opinions of the number of people you polled and nothing more. If you attempt to extrapolate non-stratified findings to the population at large you will be asking for trouble.
      You may want to check Cochran – Sampling Techniques – Wiley for a discussion of the issues surrounding sampling methods and sample size.



    I agree with what everyone else has said about stratifying your customers and therefore stratifying your sample across customer segments.
    For a quick sample size calculator I use this site:
    To generate randome non-duplicating numbers, I use this site (May be helpful in picking the participants):


    shree nanguneri

    Hi Janessa:
    It looks like you have the right answers on your sample size needs.  Have you already confirmed that the survey is an established need?  In other words do you have a strong evidence indicating that the surveying activity or the results from the surveying activity is critical to some pre-defined need?
    Often times people set out on a survey and may or may not have the tool to establish that the survey itself is a critical need.  Is this something that you have already assessed?  Looks like you have but just wanted to verify.  If you haven’t there is a tool to get there and it may save you a lot of effort.

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