It's ignoring the contribution of intelligence, grit, and other factors to _getting_ into this situations (whether casually or correlatively). As an easy examp

It's ignoring the contribution of intelligence, grit, and other factors to _getting_ into this situations (whether casually or correlatively). As an easy example: if I independently studied kindergarteners, fifth graders, and twelfth graders, I will have might discover that age has no correlation with verbal proficiency. The problem is that by studying homogeneous groups separately, I've thrown away the possibility of studying the effects that may have induced the homogeneity.