The erratic and minimal contribution of women fifteen to nineteen is a constant source of distortion; inclusion of women over the age of forty who represent declining natural fertility and diminished sexual activity further complicates the validity of the measure. In 1977, at the same time that the Area Fertility Survey program of annual demographic measurement was initiated, a new population control strategy was begun by the Philippine Population Commission. The direct determinant of fertility is contraception, which directly affects the total marital fertility rate (TMFR). The largest drop in marital fertility associated with effective contraception is in the thirty to thirty-nine age group. The impact of contraception should be assessed by separating users into age groups. The indicated conclusion is that changes in TMFRs which may result from family planning practise might best be investigated by seeking to relate age-specific use of effective methods to corresponding age-specific marital fertility rates.