For animal related clinical trials calculation of sample size is very important. For Animal studies sample size can be calculated on following two basis.
1] Based on testing the hypothesis:
II] Based on Resource Equation Method:
1] Based on testing the hypothesis:
For calculation of sample size based on testing the hypothesis required prerequisites such as standard deviation, effect size etc. If information of prerequisites for calculation of sample size is available in literature then appropriate formula of sample size calculation can be used.
But in certain situations it is not possible to get information related to the prerequisites for calculation of sample size. In this situation sample size can be calculated using resource equation method.
II] Based on Resource Equation Method:
Resource Equation Method is depends up on the size of whole experiment and the number of treatments groups. For animal studies we required optimum sample size so in this Resource Equation Method E is calculated based on decided sample size. For optimum sample size, the value if E should lies within 10 to 20 samples.
If a value of E is less than 10 then more animal should be included and if it is more than 20 then sample size should be decreased.
E = ( Total number of animals) – (Total number of groups ) [ 10 < E < 20 ]
For Example : Suppose in an animal study a researcher formed 5 groups of animal having 7 animals each for different interventions then total animals will be 35 (5 × 7).
So E = 35– 5 = 30 (i.e. 30 is more than 20 hence animals should be decreased in each group).
So if researcher takes 4 rats in each group then E will be E = 20 – 5 = 15
E is 15 which lies within 10 20.
Hence four rats per group can be considered as appropriate sample size.
This is a crude method and should be used only if sample size calculation cannot be done by power analysis method. If Study having more than two groups then it is difficult to specify effect size of study so in that situation power analysis is not easy to use.
