How to calculate the right sample size for pilot study?
The survey instrument that I am trying to develop will have some adapted items (these have their reliability and validity checked) and some modified items and some developed by me based on previous published literature. But there no information available for if the items in these published work were checked or not using survey.
So I think I need to do both EFA and CFA to validate my instrument.
Please advise on how to decide\ CALCULATE the pilot study sample size.
Thanks and regards,
Rekha Mishra
Dear Rekha,
Thank you very much for this very interesting question. I personnally think that sample size in a pilote study should not be a major worry because pilote study are usually designed to assess the feasibility of a particular methode and to generate necessary information that can guide similar research in future. If you can find some elements in the literature to calculate the sample size, then it is ok and you should not go ahead to test the reliability and the validity of these elements before use. I hope I have given some elements of the response to your question.
If the survey instrument to be used has been adapted and further developed to incorporate other theoretical contributions, you must perform an initial validation study of the new survey instrument. I agree with Martin that the pilot study should serve to assess the feasibility of the method, ie whether the planned procedures are feasible without measuring instruments. In that sense the sample size should allow you to assess the skills of interviewers or people who apply the survey instruments (2 or 3 observations per person)
The pilot study usually is not designed to estimate the sample size, but mostly it is preliminary examination for the questionnaire clarity, readability, feasablilty etc. In addition to estimate the the needed time, and potential difficulties in its application.
The sample size in piloting has varied answers in textbooks,, the range of estimation is between 5-10% of the actual study sample.
Good luck
– A pilot study is a preliminary study intended to test the feasibility of a larger study, data collection methods, collect information for sample size calculations, and therefore should always have a main study to which it leads.
– In other words, pilot studies cannot exist on their own, but only in relation to a larger studies with the aim to facilitate the larger studies.
– A pilot study SHOULD NOT be regarded as a study which is too small to produce a definitive answer to the question of interest.
An integrated confirmatory and exploratory factor analysis approach (CFA and EFA, respectively).
http://www.humankinetics.com/acucustom/sitename/Documents/DocumentItem/05Block_184-205_ej.pdf
Pilot studies are very helpful in providing insights into some of these issues
• good planning: devise a clear plan of how to monitor recruitment. This may also help the proposal for funding since funders may well be impressed by a proposal which shows that this issue has been considered by applicants and some there are plans to deal with it
• request to the funders for an extension in time or for an extension in funding
• check with potential collaborators what their other trial commitments are
• maintain regular visits to trial sites and good contact with staff who are responsible for recruitment
• to have recruitment targets (milestones) to enable the research team to monitor how well recruitment is going, so that problems can be detected as soon as possible
https://fammedmcmaster.ca/research/files/sample-size-calculations
In general the determination of the right sample size depends on the statistical methods you use. If the cost of each sample unit is not much then one can take over 30 and use normal approximations when are needed.
Look also the following papers:
Design and analysis of pilot studies: recommendations for good practice
http://onlinelibrary.wiley.com/doi/10.1111/j..2002.384.doc.x/full
Organizational Research: Determining Appropriate Sample Size in Survey Research
ftp://149.222-62-69.ftth.swbr.surewest.net/TreePDF/Determing%20Appropriate%20Sample%20Size%20in%20Survey%20Research.pdf
Dear Rekha
Specifically, among the above researchers' comment, I go with "Costas" ... "the right sample size depends on the statistical methods you use". For constructed items, ensure content and face validity through a panel of expert (not for adopted or adapted items) than you can only take minimum 30 and above respondents for testing your instrument who will not be included in your subsequent actual study, as simple as I say. Enjoy your project.
Dr. Aktar
generally, researcher used the sample of 30 for the pilot study, so i think you can also proceed with the sample of 30
Pilot study
Saunders et al., (2007) state that prior to using the questionnaire to collect data it should be pilot tested. Saunders et al., (2007) point out the purpose of the pilot test is to refine the questionnaire so that the respondents will have no problems in answering the questions and also there will be no problems in recording the data
Fink (2003b) as cited in Saunders et al., (2007) state that the minimum number for a pilot study is 10.
For the main study
Sekaran (2003) wrote:
Roscoe (1975) proposes the following rules of thumb for determining sample size:
1. Sample sizes larger than 30 and less than 500 are appropriate for most research.
2. Where samples are to be broken into subsamples; (male/females, juniors/
seniors, etc.), a minimum sample size of 30 for each category is necessary.
3. In multivariate research (including multiple regression analyses), the sample size should be several times (preferably 10 times or more) as large as the number of variables in the study.
4. For simple experimental research with tight experimental controls (matched pairs, etc.), successful research is possible with samples as small as 10 to 20 in size.
References
Sekaran, U., 2003. Research methods for business: A skill building approach. John Wiley & Sons.
Saunders, M.N., 2007. Research methods for business students, 5/e. Pearson Education India.
Pl have a look at the following RG link:
https://www.researchgate.net/post/How_much_Should_be_the_Sample_Size_for_Pilot_Study
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