  Multivariate methods that relate outcomes to risk factors have been adopted
clinically to individualize treatment. This has promoted the belief that
individuals have a true or unique risk.
  The logic of assigning an individual a single risk value has been criticized
since 1866. The reason is that any individual can be simultaneously considered
a member of different groups, with each group having its own risk level (the
reference class problem).
  Lemeshow et al. provided well-documented examples of remarkable discordance
between predictions for an individual by different valid predictive methods
utilizing different risk factors. The prevalence of such discordance is unknown
as it is rarely evaluated, but must be substantial due to the abundance of risk
factors.
  Lemeshow et al. cautioned against using ICU mortality predictions for the
provision of care to individual patients. If individual risk estimates are used
clinically, users should be aware that valid methods may give very different
results.
