Find out if your proposed study has enough power.
Use the calculator below to see how these factors affect study power:

To calculate study power, choose a value for each factor by moving the sliders with your mouse or entering numbers into the boxes above a slider and then pressing ENTER.

Sample
Size		 Exposed
with disease
 Unexposed
with disease
 Study
Power
  people in the Exposed group
  of them developed the disease after exposure (1)
  people in the Unexposed group
  of them developed the disease without receiving exposure (2)
Assumptions
  Exposed must be greater than or equal to Unexposed  
Equal number of people in Exposed and Unexposed groups
Level of significance is 5% or less
Calculation is for a two-sample test for binomial proportions
Sample Size must be large enough for this statistical test to be valid
Calculator will only accept whole numbers as input
(1) Click here for examples of disease rates in populations not exposed to contaminants.
(2) Click here for examples of how much the rate of disease increased due to exposure
      to contaminants according to health studies conducted in the past. Relative risk is how
      many times greater the disease occurrence in the exposed group is compared to the
      unexposed group.
More Study Power is Better
More study power is desirable because this means that the proposed study is more likely to find an association between exposure and illness, if it exists. There is no set, specific value for study power that must be achieved in order to conduct a health study. However, researchers often want to make sure that their proposed study has at least 80% or 90% power. With that in mind, here is how to interpret the output from the calculator:
Calculated Study Power Meter Color Is This Study Power Acceptable?
80% or Greater Green Probably Yes
70% to 80% Yellow Probably Not
Less Than 70% Red No
N/A Red Your sample size is not large enough for the statistical test used in this type of study to be valid. Therefore, study power could not be calculated.