The following formulas are for the negative log-likelihoods to fit common parametric models. Each formula uses the calculator if conditional function with the uncensored case of the conditional first and the right-censored case as the Else clause. You can copy these formulas from tables in the Loss Function Templates folder in Sample Data and paste them into your data table.

In the exponential loss function shown here, sigma represents the mean of the exponential distribution and Time is the age at failure.

There are examples of one-parameter, two-parameter, and extreme-value functions in the Loss Function Templates folder.

The formula shown below is the lognormal loss function where Normal Distribution(model/sigma) is the standard normal distribution function. The hazard function has value 0 at t = 0, increases to a maximum, and then decreases. The hazard function approaches zero as t becomes large.

If Y is distributed as the logistic distribution, Exp(Y) is distributed as the loglogistic distribution.