Patented is a method of determining effectiveness of an illustration for a diaper during a diaper changing process. The diaper comprises a main body for being fitted onto a body of an infant and a first illustration displaying part provided on the main body for displaying a first illustration. The illustration is determined based on the age in months of the infant. A second illustration display part displays a second illustration. The first illustration and the second illustration express a change of a behavior of a character, an irreversible transition in time, a change near the hands of a character, a change of scene, a movement of a character, a change of expression, or an irreversible transition in time and a growth process. The first illustration and the second illustration are mutually relevant or integrated as a whole in terms of shape, pattern, color, concept, or a combination thereof. The method comprises the steps of: (a) during the diaper changing process and while showing at least one of the first and second illustrations to the infant whose diaper is to be changed, (a1) monitoring signals made by an exchanger and the infant, and (a2) measuring the duration of each the signal, (b) calculating an exchanger approach value by (b1) for each signal made by the exchanger and indicative of the exchanger’s positive emotion, calculating an exchanger positive time value as a product of the duration of the signal multiplied by a positive exchanger signal value, (b2) for each signal made by the exchanger and indicative of the exchanger’s negative emotion, calculating an exchanger negative time value as a product of the duration of the signal multiplied by a negative exchanger signal value and (b3) calculating the exchanger approach value as a sum of the exchanger positive and negative time values, (c) calculating an infant response value by (c1) for each signal made by the infant and indicative of the infant’s positive emotion, calculating an infant positive time value as a product of the duration of the signal multiplied by a positive infant signal value, (c2) for each signal made by the infant and indicative of the Infant’s negative emotion, calculating an infant negative time value as a product of the duration of the signal multiplied by a negative infant signal value and (c3) calculating the infant response value as a sum of the infant positive and negative time values, (d) calculating a positive action value as a sum of the exchanger and infant positive time values, (e) calculating an interaction value as a sum of the exchanger approach value and the infant response value and (f) evaluating the effectiveness of at least one of the first and second illustrations based on at least one of the positive action value and the interaction value.