# Thread: Power, effect size, sample size explanation

1. ## Power, effect size, sample size explanation

Would someone please explain or provide a link to an explanation for the following quote:
When planning a study, practicing researchers specify an expected
(standardized) effect size and desired Types I and II errors to
calculate the required sample size. The process of power calculation
can be reversed to compute the sample size from estimates of effect
size.
The quote comes from an article in which I was attempting to learn how to use the pilot study to determine a sample size.

After having read so many articles, books, websites, etc -- I am absolutely lost and confused. Everyone uses different words to describe similar ideas - and somehow the reader is expected to figure it out. In other words, my brain is dull - what the HECK does the author mean? Are we to just "naturally" know how to calculate sample size from the pilot study?

Thank you for your time. Hopefully you didn't laugh too hard.

2. I know where you are coming from. By doing a pilot study you are able to estimte the amount of variability in the system and therefore calculate, based on the mean and variance of the pilot study, how many samples you would require to achieve a set (by yourself or clients) level of power form you results (i.e. do you wnat to be within 5, 10 or 20 % of the true population estimate).

I come from a biology background, that aside, I suggest you google "STREAM PERIPHYTON MONITORING MANUAL" the second on the list should be the PDF (Sorry its too larger to upload here) look at this PDF starting on page 16, it is a really exellent background to all of this, with formulae in clear easy to understand explanations.

Phil

3. Thank you for the link. I started reading on page 16, section 3.

4. ## Re: Power, effect size, sample size explanation

Originally Posted by bugman
......I suggest you google "STREAM PERIPHYTON MONITORING MANUAL" the second on the list should be the PDF (Sorry its too larger to upload here) look at this PDF starting on page 16, it is a really exellent background to all of this, with formulae in clear easy to understand explanations.