Statistical considerations for a cross-over study where the outcome is a measurement

Note: The power calculation uses the non-central t function, pt(x,df,ncen), and it's inverse qt
Power=pt(qt(.025,n-1,0),n-1,-(delta/sigma)*sqrt(n)), power is truncated rather than rounded. The parameter sigma is the standard deviation of the difference which is sqrt(2) times the within patient standard deviation.
If power is specified the other parameters are found by searching.


Significance Level (%) — sided (default is 0.05, two-sided)

Within patient standard deviation (if known), or Standard deviation of the difference between the two value for the same patient (if known)

Enter two of the following three values and the remaining value will be calculated

  1. Total number of patients
  2. Power (usually 0.8 or 0.9)
  3. Minimal detectable difference in means

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This software developed by David Schoenfeld, Ph.D. (, with support from the MGH Mallinckrodt General Clinical Research Center. Javascript version developed by REMorse.

These calculations are based on assumptions which may not be true for the clinical trial that you are planning. We do not guarantee the accuracy of these calculations or their suitability for your application. We suggest that you speak to a biostatistical consultant when planning a clinical trial. Please contact us if you have any questions or problems using this software