Perhaps the most frequently asked question that we receive is, “What sample size do I need?”. The answer to this question is influenced by a number of factors, including the purpose of the study, population size, the risk of selecting a “bad” sample, and the allowable sampling error.
In order to best estimate the sample size that you’d require or to validate that the sample you’ve planned is sufficient, we would conduct a power analysis for your study. To do this, we’d either refer to any pilot data you may have collected (the best choice), or to parameters in the relevant literature (if you’ve not done a pilot test). If you have a very esoteric study and neither of those options is reasonable, then we would use “rule of thumb” values for the effect sizes.
There are three major considerations when doing a power analysis for sample size determination, and we will consider all of these things while doing your power analysis:
We also can conduct power analyses on more complex psychometric studies using structural equation modeling. For this type of study, we would need details on how you plan to set up the SEM (latent variables, their indicators, their correlations, etc.). We then conduct the power analysis based on the methods described in McCallum, Browne, Sugawara (1996, also cited in the Klein’s SEM text ‘Principles and Practices of Structural Equation Modeling’). This method involves performing a custom SAS routine for calculating power and sample size needed in order to accept or reject the null hypothesis that the model is a good fit of the data, based on the Root Mean Square Error of Approximation (RMSEA) metric.
If you require a power analysis at this stage of your project, we can ordinarily provide this for you within 1-2 days. Please call or email to discuss your project.
We understand the importance and necessity of confidentiality, and provide all of our prospective clients with a Non-Disclosure Agreement immediately upon contact. This ensures you that your research will not be shared with any third parties, and your consultation with us is completely confidential.