WASET
    Ching-I Chen,  Associated Map and Inter-Purchase Time Model for Multiple-Category Products.   journal   = {International Journal of Economics and Management Engineering}, [online]. World Academy of Science, Engineering and Technology.
    April 2014, vol. 89(5). 1440 - 1444
    [viewed 16 April 2024]. Available from: https://publications.waset.org/pdf/9998268.