Table 3.

Year-to-year changes in mean industry payments per prescribing physician.

Years since approval	N (%)	Mean year-to-year change	Median year-to-year change	Generic within 3 years, N (%)	Estimated year-to-year change in ratio, no generic	S	P-value	Estimated payments in year +1, if payments in index year = $1000
0-4 years	105 (39)	0.82	0.75	1 (1%)	−0.366	0.072	<.0001	$681
5-9 years	84 (31)	1.14	0.81	5 (6%)	−0.188	0.116	.103	$825
≥10 years	78 (29)	0.94	0.80	28 (36%)	−0.370	0.131	.005	$679

Each observation represents the relative change from the index year to the subsequent year, expressed as the ratio of mean, per-prescribing-physician industry payments in the subsequent year to the index year, with 1.0 representing no change. The observation set therefore reflects the subset of drug-calendar year pairs in which the drug was also observed in the subsequent year (N = 267, unique drugs = 85). Observations were grouped according to the number of complete calendar years since approval as of the index year, and generalized estimating equations were used to estimate the year-to-year change associated with each category of years since approval. P-values represent a test for whether year-to-year change was statistically significantly different than the null value of 1. The point estimate for the year-to-year change was used to estimate the dollar value of subsequent-year payments assuming $1000 per prescribing physician in the index year and no generic competition within 3 years.