Let's not overthink this one. Everton scored four goals in the six games before Donovan arrived, going 2-2-2 across all competitions. Since January 4, they've scored 11 in nine, going 4-3-2 with wins over Manchester City and Chelsea.
In January, Everton scored eight times. Donovan assisted five of them.
Somewhere, Robbie Keane and Edson Buddle are smiling.