2. Sample Size Calculation – Basic Formula

Introduction to Sample Size Calculation
Training session with Dr Helen Brown, Senior Statistician, at The Roslin Institute, January 2016.
************************************************
These training sessions were given to staff and research students at the Roslin Institute. The material is also used for the Animal Biosciences MSc course taught at the Institute.
************************************************
A spreadsheet to carry out the calculations described in the presentation may be copied here: http://datashare.is.ed.ac.uk/handle/10283/1996
*********************************************
*Recommended YouTube playback settings for the best viewing experience: 1080p HD
************************************************
Content:
Sample size calculation
Calculate it such that there is a good chance of achieving study objectives
Depends on several factors:
---Size of difference (?) to detect, minimal effect of interest
- Eg a 50% decrease in gene expression
---Significance level (a) (eg 0.05)
---Power (ß) = chance of detecting a significant result if true difference is ?
(typically 80%, 90%)
---Standard deviation (SD or s) of data (how much variability)

Basic formula for sample size - Continuous data
Where ? = size of difference, minimal effect of interest
a = significance level (eg 0.05)
ß = power, probability of detecting a significant result (typically 80%, 90%)
s = SD of data
Zp = points on normal distribution to give required power and significance

Most suitable for data assumed to be normally distributed
Non-normal continuous data :
---no ideal formula
---above formula often suitable as it tends to be conservative
(due to SDs tending to be large in non-normal data)

Z-values are from the Normal distribution

Видео 2. Sample Size Calculation – Basic Formula канала The Roslin Institute - Training