There are many assumptions regarding the treatment utility of assessme
nt that are not supported by objective data We identify and discuss th
ree of these assumptions: (a) aptitude-treatment interactions do not (
and never will) provide a valid basis for treatment selection; (b) ind
ividualized assessment is better than non-individualized assessment; a
nd (c) assessment (e.g., functional assessment) improves consultation
treatments. These assumptions are myths, because they are not (yet) su
pported by objective, data-based research. We conclude our discussion
of treatment utility myths by proposing a research agenda that would p
rovide an objective, data-based body of research to clarify whether ps
ychologists should retain or reject these assumptions.