I am conducting a research containing a questionnaire survey. Respondents are required to responds to two attitudes ( probability of occurrence and degree of impact) based on five points likert scale. which equation should be used to determine sample size?
Hi Mohammed
There are several methods could be use to determine the sample size of the study:
1- Krejcie and Morgan table(Krejcie, R. V., & Morgan, D. W. (1970). Determining sample size for research activities. Educational and psychological measurement, 30(3), 607-610).
2- Range Rule of Thumb 30 to 500
3- Use previous studies results(mean and standard deviation)
4- Use raosoft website -http://www.raosoft.com/samplesize.html
So, u can either consider ur population or previous related studies to calculate ur sample size.
I hope this can help u.
Best regards
Kindly read about and download this (GPower) here: http://www.gpower.hhu.de/
Hi Mohammed
There are several methods could be use to determine the sample size of the study:
1- Krejcie and Morgan table(Krejcie, R. V., & Morgan, D. W. (1970). Determining sample size for research activities. Educational and psychological measurement, 30(3), 607-610).
2- Range Rule of Thumb 30 to 500
3- Use previous studies results(mean and standard deviation)
4- Use raosoft website -http://www.raosoft.com/samplesize.html
So, u can either consider ur population or previous related studies to calculate ur sample size.
I hope this can help u.
Best regards
Yes, the data should be atleast 300 to apply most of the statistical techniques.
There is a formula also:
Sample Size
ss =Z 2 * (p) * (1-p)c 2
Where:
Z = Z value (e.g. 1.96 for 95% confidence level) p = percentage picking a choice, expressed as decimal (.5 used for sample size needed) c = confidence interval, expressed as decimal (e.g., .04 = ±4)
https://www.surveysystem.com/sample-size-formula.htm
Thank you for your contributions
the problem is, I have three groups and every on of each contain approximately 2000 persons. how can I identify the minimal number of each group in order to reduce the time needed for the information related to each group to be fed into excel or SPSS and making analysis.
Hi Mohammad,
Adding to previous excellent responses, you could also use PS, one of the most popular free tool to calculate power and sample size for various types of studies. Link below. Hope this helps. Best regards, Hanif.
http://biostat.mc.vanderbilt.edu/wiki/Main/PowerSampleSize
Hi Mohammad!
First, you may go through the previous articles related on your field to get some kind of idea to determine the sample size primarily; secondly, use the previous studies' mean and standard deviation to calculate your sample size through a software. There are few out there, my recommended one is: https://www.dssresearch.com/KnowledgeCenter/toolkitcalculators/statisticalpowercalculators.aspx
Add more information, I think it doesn't matter how many group you have, follow through the procedure based on the information of SD in the article:
t- test, SD, and n= ? (will tell you how many you need in each group. Here is one more calculating software: http://powerandsamplesize.com/
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