No, but you need to make the investigation large enough so that it will be precise enough.
You have not told us anything about what you want to investigate so it is difficult to suggest anything.
Suppose that you have a scale with 5 levels, like: 1, 2, 3, 4, 5 and that the standard deviation is 1.
You need to make the sample size n large enough.
mean +/- 2*s/sqrt(n)
"sqrt" is supposed to be square root.
Suppose the mean of your study would be 3.5 then what is the margin of error? Suppose you used n= 25. then the margin of error would be:
3.5 +/- 2*1/sqrt(25) = 3.5 +/- 0.4 so that the interval would be 3.1 up to 3.9. Would that be precise enough?
Or suppose you had n=100 then it would be 3.5 +/- 2*1/sqrt(100) =3.5 +/- 0.2 with interval 3.3 up to 3.7. Good enough?
It is up to you to choose a big enough sample that is precise enough for your needs.
this is more for others who may read this thread in the future. i got a good statistician from Elance. He is very experienced and was not charging the earth so happy about this. cheers!
I take the opportunity to quote myself:
Was £50 enough for this statistician?You also do it right in that you show a willingness to pay for the service the statistician can do for you. (A messy study can be changed to a clear cut study, if planned correct from the start.) If you, your supervisor and your department start a long run cooperation with a statistician, that can turn out to be one of the best investments you have ever made.
It would be nice if you told us the result from this study.
@brownbabygirl,
Determining the sample size depends directly on what is your survey's question, meaning, what do you plan to test ? If you plan to run a t-test, there a way to calculate a sample size for this case. If it's another test you are after, a completely different way.
You need to describe your survey, the data you plan to collect, and most importantly, what is the aim of the study: are you going to make inference on some population ? Are you going to compare means of 2 populations (or more ?), are you going to compare proportions ? Or perhaps time to event ? You put this question in a biostatistics forum, is it related to medicine ? Lot's of data that the statistician needs to know in order to assist you.
There are software solutions for sample size, some are simple and free (Gpower, PS,...), some cost money (PASS). The thing is, if you do not know what you are doing, possessing a software solution will be of no help at all. Same goes for the analysis, there is a free solution: R, but it ain't easy. Maybe you can get from your university an access to another packages like SAS or SPSS.
brownbabygirl (08-19-2014)
You have data analysis tool in excel to make the t-test in a even easier way
Tweet |