WASET
    Toni Raurich and  Joan Llonch-Andreu,  Pay Per Click Attribution: Effects on Direct Search Traffic and Purchases.   journal   = {International Journal of Economics and Management Engineering}, [online]. World Academy of Science, Engineering and Technology.
    December 2022, vol. 192(12). 811 - 821
    [viewed 24 April 2024]. Available from: https://publications.waset.org/pdf/10012849.