The lag effects from DTC are very complex. How did you determine that there is a 2-year effect if the impact of DTC was not significant in the first place?
The Koyk-lag was used for DTC as well as the others. Indeed the effect might be more complex, and this would be an avenue for further investigation. The grid search found a lambda of .9 for DTC and, given this lambda, one can obtain the confidence intervals for the effects, and therefore the statistical significance. Note the uncertainty in lambda is not explicitly considered in these confidence intervals which probably makes these intervals conservative. 58. The issue of the lags is complex. I can easily believe that a detail has a lag of up to 3 months, an event has a lag of about 6 months, and a journal ad a lag of about 1 month. But I am unsure about DTC because it may take a considerable amount of time for a patient to see the ad, make an appointment with the physician, talk to the physician about the product, and get a prescription. The amount of time is probably random for a patient in a way that it is not random for a physician. The easiest way around that problem is to use lon
