Kru Somsri's English School

eling in general and with the problem of measuring the carryover effect in particular.
Among them are:
   
   1.There is often little variation in advertising except that due to seasonable factors. without variation in
   advertising it is not possible to detect the impact ofchanges in advertising on sales. This problem is
   severe when a brand is overadertising and it is so far out on the advertising response curve  that there
   is no response ti any change in advertising. In that case an extreme drop in advertising would be
   needed to detect any response, and such avariation is simply not in the data

               
   2.The data may be faulty. For example, accounting sales data will represent shipments to retailers and
   not consumer purchases in response to advertising. Syndicated store movement data overcome this
   problem but are expensive and available only to consumer products firms. Accounting advertising data
   similarly represent billings bu anasency and not exposures ti ads. In fact, it isdifficult to get any accurate
   measure of advertising exposures.


   3.Data describing other marketing variables are often not available or are expensive to obtain. Data
   describing competitor activities are rarely available. Annual data really are inadequate since the
   immediate and carryover effect of advertising usually occurs in months, not years.


   4.if abusiness uses the percentage-of-sales method of  establishing a bud,a sales change could cause
   a change in advertising expendi tures in stead of the reverse (at least annual level).
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