Which of the following is not a traditional factor considered in mortgage approval?

The choice of family size as a factor not traditionally considered in mortgage approval is based on the conventional practices of lenders when assessing an applicant's qualifications. Traditional mortgage approval criteria primarily focus on quantifiable financial metrics that directly impact an applicant's ability to repay the loan.

Credit score is a crucial element since it reflects the borrower's creditworthiness and history of repaying debts. Income is also vital, as it helps lenders evaluate whether the borrower earns enough to afford the mortgage payments. The debt-to-income ratio provides a clear picture of how much of an applicant's income is already allocated to existing debts, helping lenders determine risk in extending further credit.

In contrast, while family size may influence an individual's financial responsibilities and housing needs, it is not standard in the calculation of a borrower's credit risk or repayment ability directly. Therefore, it does not fit within the core financial metrics lenders typically analyze in mortgage approvals, making it the correct choice.