Hello Samantha,

In the absence of extant studies which report on observed effects of the type you wish to investigate, there are several other viable options:

1. Run a small, pilot study to get an idea of what effects may exist. Note, though, that the effects which may exist might or might not be considered worthy of attention (as in the next suggestion).

2. Get a consensus value from a group of domain experts as to what magnitude of effect would be noteworthy, should it exist in the population.

3. Evaluate the effect from an economic basis: At what magnitude of effect would the resultant costs (considering both positive and negative) outweigh those of no treatment/measurement/diagnosis.

Good luck with your work.

In scientific investigations, determining the sample size is one of the most important aspects of a study’s scientific contribution. For, the sample size has a significant impact on the proposed hypothesis and the adopted study design. That being highlighted, there is no point-blank way to specify the effective sample size for reaching a reliable result. The review by Serdar et al. (2021), fully cited below, could interest you.

Serdar, C. C., Cihan, M., Yücel, D., & Serdar, M. A. (2021). Sample size, power and effect size revisited: Simplified and practical approaches in pre-clinical, clinical and laboratory studies. Biochemia Medica, 31(1), 27–53. https://doi.org/10.11613/BM.2021.010502

Article Sample size, power and effect size revisited: simplified and...

Good luck,

The samples’ size can be estimated based on the size of the population, confidence level, margin of error and response distribution, etc. For larger populations, E. Johansson et al (2014) have suggested an acceptable sample size ranging between 400-500 individuals. The number of survey samples required corresponding to various confidence levels and margin of errors can be derived based on recommendations by (Thompson, 1987) and (Holmes, Illowsky, & Dean, 2015) for binomial and multinomial data.

Hope this helps