Modeling human neurobehavioral functions has the goal of identifying work-r
est schedules that are safer and more productive. The models of Folkard et
al. and of Jewett and Kronauer illustrate excellent progress toward this go
al. Examination of these models reveals four additional areas that need to
be addressed to facilitate continued development of accurate models of neur
obehavioral-functions. (1) The choice of neurobehavioral metrics may have a
significant influence on model development. The lack of correlation among
different neurobehavioral measures may make comparisons of models difficult
. Many neurobehavioral measures are confounded by secondary and random erro
r variance that can lead to model distortion. Although different models may
ultimately be required for different neurobehavioral functions, measures t
hat have been extensively validated to be sensitive to circadian variation
and sleep loss should take priority in model development. (2) Because error
variance in neurobehavioral outcomes can be substantial in uncontrolled en
vironments, model validation should proceed from controlled laboratory prot
ocols to real-world scenarios. Once validated, the ability of a model to pr
edict field data can be tested. (3) While neurobehavioral models have been
developed to predict behavior over time (i.e., within-subjects), to be usef
ul in the real world, models will also ultimately have to provide estimates
of between-subject variation in vulnerability to neurobehavioral dysfuncti
on during night work or sleep loss (e.g., younger versus older workers). (4
) Finally, to be theoretically accurate and practically useful, models of h
uman neurobehavioral functions should be able to predict both cumulative ef
fects (i.e., across days or weeks) and the influence of countermeasures (e.
g., light, naps, caffeine).