Step 1: Write marketable surplus as total production minus the quantity retained for family needs.
Step 2: Size of holding, quality of production, and higher resources all push the production term up, so they raise marketable surplus, giving them a positive relationship.
Step 3: Size of family pushes the retained for consumption term up instead, which pulls marketable surplus down, making it the one factor with a negative, not positive, relationship.
\[\boxed{\text{Size of family}}\]