GMAT Critical Reasoning (CR) | Artistic success as an actor is directly dependent on how well an acto

Artistic success as an actor is directly dependent on how well an actor has developed his craft. This has been demonstrated by the discovery of a positive relationship between the number of classes taken by an actor and the number of professional production in which that actor has appeared in the past two years.

Each of the following, if true, casts doubt on the author’s argument about artistic success for actors EXCEPT:

(A) The figures for the number of classes taken were based solely on