Modelling consumers' use of products

Patterns of consumers' use of products are of interest to manufacturers. Th is paper is concerned with modelling diary data on the use of one product. shampoo, recorded to the nearest hour by over 500 men during 1 week. A bina ry response multilevel model is developed, building on similar models for c onsumer purchase data. The model allows for a dependence on the number of d ays since last use. The results of fitting Various Versions of this model a re discussed. A problem is that the number of days since last use is missin g for all times up to the first use. An approximate EM approach is consider ed to deal with this problem.