Biomedical Engineering Reference
In-Depth Information
Table 22.4 Estimation results
Pre-peak window
Post-peak window
All years
Intercept for class
effects ( α 0 )
5.8704
6.5475
5.8740
(59.40)
(45.42)
(86.72)
PPI class dummy
−0.4478
0.0499
−0.4082
(−3.49)
(0.36)
(−4.07)
SSRI class dummy
−0.2790
−0.8565
−0.2835
(−2.46)
(−5.99)
(−3.03)
Intercept for promo
tion effects ( β 0 )
−2.4436
−3.2831
−2.5781
(−6.19)
(−10.08)
(−7.80)
DTCA
0.0020
−0.0007
0.0019
(3.00)
(−3.51)
(3.26)
DET
0.0028
0.0018
0.0030
(3.87)
(5.26)
(5.15)
PJA
0.0052
0.0295
0.0047
(0.99)
(3.74)
(0.98)
R 2
0.5294
0.8867
0.5987
t -Values in parenthesis
where S , DTCA, DET, and PJA stand, respectively, for sales, DTCA, detailing, and
PJA (all measured in dollars) for drug i in year t of window j and D 1 and D 2 represent
the dummy variables for PPI and SSRI classes, respectively. Preliminary analysis
suggested that the other promotional variables do not have a significant effect and
were subsequently dropped from the model to ease exposition. Note that there are
two intercept terms, one ( α 0 ) for the class effects and one ( β 0 ) for the promotional
effects.
Table 22.4 contains the results of the analysis for each of the three windows (pre-
peak, post-peak, and all years). In general, detailing and PJA are more effective than
DTCA (“All years” column), confirming previous empirical findings, but in the pre-
peak window the gap in effectiveness, particularly between DTCA and detailing, is
smaller. This is not surprising since the window covers the deregulation period
where DTCA was considered as a novelty and hence a larger effect is expected.
However, in the post-peak period the situation dramatically reverses for DTCA
which has a small but significant negative effect (Figs. 22.7 , 22.8 , and 22.9 ). This
clearly suggests that DTCA influence fatigue which is consistent with informational
effects, since these tend to occur earlier in the life cycle (e.g., Kolsarici and Vakratsas
2010 ), as previously discussed studies also indicated. It further suggests that DTCA
is not a major driver of drug sales as it cannot reverse the sales decline after 2004,
but it rather seems to contribute to it with its negative effect. It should be noted that
this post-peak oversaturation of DTCA effects cannot be attributed to excess expo-
sure to DTCA since average expenditures decreased post-peak (Table 22.3 ). On the
other hand, detailing and PJA continue to have a significantly positive effect on
sales post-2004, which, along with the greater magnitude of the corresponding
 
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