Table 3.

Segmented regression analysis in relation to PDI guideline publication, reference groups

Medicine group (preferred drug)	Guidelines introduced	Percentage of preferred drug items: Jan−March 2011 (SE), 95% CI	Increase in % of preferred drug items per quarter post March 2011 (SE), 95% CI, P value	Increase in % of preferred drug items April−June 2013*, (SE), 95% CI, P value	Increase in % of preferred drug items per quarter post June 2013, (SE), 95% CI, P value	Increase in % of preferred drug items Oct−Dec 2013†, (SE), 95% CI, P value	Increase in % of preferred drug items per quarter post Dec 2013, (SE), 95% CI, P value	Increase in % of preferred drug items April−June 2014‡, (SE), 95% CI, P value	Increase in % of preferred drug items per quarter post June 2014, (SE), 95% CI, P value	Increase in % of preferred drug items Oct−Dec 2014§ (SE), 95% CI, P value	Increase in % of preferred drug items per quarter post Dec 2014, (SE), 95% CI, P value
Beta-blockers (bisoprolol)	September 2016	51.20 (0.03), (51.15 to 51.26)	0.53 (0.01), (0.52 to 0.54), P<0.001	−0.02 (0.05), (−0.13 to 0.09), P=0.71	0.50 (0.02), (0.45 to 0.54), P<0.001	–	–	−0.05 (0.06), (−0.18 to 0.08), P=0.44	0.41 (0.001), (0.40 to 0.42), P<0.001	–	–
Calcium channel blockers (amlodipine)	September 2016	68.18 (0.03), (68.12 to 68.29)	−0.34 (0.01), (−0.35 to –0.33), P<0.001	–	–	0.12 (0.06), (−0.001 to 0.23), P=0.06	−0.26 (0.02) (−0.31 to –0.21), P<0.001	–	–	0.02 (0.07), (−0.13 to 0.17), P=0.76	−0.21 (0.01) (−0.22 to –0.19), P<0.001

*introduction of PDI guidelines for PPIs/statins.

†introduction of PDI guidelines for ACE/ARBs.

‡introduction of PDI guidelines for SNRIs/SSRIs.

§introduction of PDI guidelines for urology medications.

ARBs, angiotensin-II receptor blockers; PDI, Preferred Drugs Initiative; PPIs, proton pump inhibitors; SNRIs, serotonin norepinephrine reuptake inhibitors; SSRIs, selective serotonin reuptake inhibitors.