In my current analysis, I have not found statistical significance to some of my conditions. So I was wondering how to predict or calculate the effect size with more subjects and items. I have 20 subjects and each have taken 120 items. My dependent variable is Reaction Time (RT) and my independent variables are Related (2 levels -- control and experimental) and PrimeType (5 levels). In testing significance, I look at RT significance of Related for each Prime Type level. For example, the significance level for PrimeType 3 when compared in RT between Related yield a p-value = .075

So I wonder what packages or functions that I could use where I put in the current observation numbers and significance level and compare it or calculate it with a bigger sample. I want to check whether the the significance level would change or become statistically significant in a bigger sample size.

Any ideas?

  • $\begingroup$ Sequential testing is inflating type 1 error rate. Thus, increasing sample size without correction for multiple testing is just cheating. $\endgroup$ – Michael M Dec 16 '13 at 6:38
  • $\begingroup$ I am trying to see whether the results changes if I have more participants, more like a prediction. In my paper, I will only share the current results and, if possible, mention how the results might or might not change with a bigger sample. As a Statistician, @MichaelMayer, what do you suggest I should do? Would re-sampling or bootstrapping decrease type 1 error rate and have a correct prediction? $\endgroup$ – ama Dec 16 '13 at 15:14
  • $\begingroup$ Resampling or bootstrapping does not directly account for multiplicity. You might get some ideas from Wiki's en.wikipedia.org/wiki/Sequential_analysis (section "Bias") about sequential testing. I hope you will find some useful links or informations about your problem. Another term related to the question is "adaptive design" or "group sequential design". $\endgroup$ – Michael M Dec 16 '13 at 15:28

The best estimate of the effect size in a larger sample is the effect size in your sample.

A large enough sample size will make any effect size statistically significant.

You can estimate this by recreating your data with the same effect size and a larger N, or by looking at the effect size in a table of p values and seeing how large it has to be in order to be significant.

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