By selecting the Fix Parameters Button on the Run Window screen, you can select parameters to "fix", or cause to not be estimated. A dialog window listing all the real parameters is presented, with edit boxes to enter the value you want the parameter to be fixed. By fixing a real parameter, you are saying that you do not want this parameter to be estimated from the data, but rather set to the specified value. Note that only real parameter values can be "fixed" in MARK -- beta estimates cannot be set to a specific value.
Fixing a parameter is a useful method to determine if it is confounded with another parameter. For example, the last Phi and p are confounded in the time-specific Cormack-Jolly-Seber model, as are the last S and r in the time-specific dead recoveries model. You can set the last p or r to 0.5 to force the survival parameter to be estimated.
For models where the real parameter estimate is a function of a single beta, the profile likelihood confidence interval endpoints can be computed by fixing the parmeter at various values until the deviance is approximately 3.84 units greater than the deviance for the maximum likelihood estimates.