Table 2.

Definition of terms.

Term	Definition
Common factor	A therapeutic/change factor that is common to all psychotherapy approaches. Also termed non-specific factor or universal factor (a-theoretical).
Specific factor	A well-specified therapeutic/change factor that is theorized to produce therapeutic benefits in a specific psychotherapy approach.
Joint factor	In this report, a therapeutic/change factor that is shared across the CATs disciplines.
Mechanism of change	A theory-driven causal chain or sequence of events or processes (or mediating variables) that explain, in greater detail than factors or mediators alone, how or why therapeutic change occurs.
Mediator	An intervening variable that is theorized to account for the statistical causal relationship between two variables, such that X causes M which in turn causes Y. A mediator clarifies how or why therapy leads to change and is a term usually used in the context of quantitative statistical analysis.
Moderator	A variable external to the treatment that influences the direction or magnitude of the statistical relationship between the treatment and outcome, such that a moderator may strengthen, weaken, diminish, or reverse the relationship between X and Y. A moderator clarifies when or for whom therapy leads to change and is a term usually used in the context of quantitative statistical analysis.

Partly based on Kazdin (2009).