Regularity, recency and rates

Survey researchers often use the recency question format-‘When was the last time you...’-to estimate purchase or usage rates. This format is particularly useful when the behavior in question is of a sensitive nature. The calculation of interpurchase times and, in turn, rates from recency format responses requires an a priori assessment of the distribution of interpurchase times. Although the usual assumption is that interpurchase times are exponential, evidence indicates that times between purchases are more regular. The authors relax the exponential assumption and measure the effects of more regular purchase behavior, discrete purchase behavior and the dead period between purchases on estimated rates. Even though the present focus is on recency, the results also give some insights into the commonly reported frequency based result that shows heavy consumers are ‘more regular’ in their purchasing behavior.