Q. Effect of past-advertisement?

Methods of evaluation advertisement effectiveness assumes that response of customers in test-area is the outcome of advertisement done in test period but actually, the response of customers may be because of past advertisement. For example if a person had seen an advertisement long ago but at that time either for the reason that of financial constraints or because of no need he didn't buy that product. However it is possible that he is carrying deep favourable impressions of that past advertisement till now. If at present he is monetary sound or need is relished then he has purchased that product. Consequently in this case sale has occurred on account on past advertisement as well as not present advertisement.