<Figure 2. Piecewise linear regression of the sign and attribution time-series for citing papers published from 1986-2019 >
For affirmational and neutral citations, a breakpoint was identified in 1996, after which the rate decreased significantly (Figure 2a). Non-attributive citations also had a breakpoint in 1996 (Figure 2b).
The time-series analysis for negational citations identified a significant breakpoint in 2004 (Figure 2a). Following that year, the number of negational citations substantially increased. Similarly, the time-series analysis for citations that attribute the opioid crisis to Portenoy’s paper had a distinctive breakpoint in 2004 (Figure 2b). After 2004, many more papers cited Portenoy’s paper as a motivating factor behind the opioid crisis.