Prescription Sequence Symmetry Analysis (PSSA) to assess prescribing cascades: a step-by-step guide

Table 3 Calculations of sequence ratios for the prescribing cascade ACEi-antitussives using different assumptions

	Study population	Patients using index before marker	Patients using marker before index	cSR	SRnull	aSR (95% CI)
Primary analysis^a	20,313	15,121	5,192	2.91	1.13	2.59 (2.56-2.62)
Washout window 6 months	29,809	22,357	7,452	3.00	1.10	2.73 (2.70-2.76)
Exposure window 6 months	16,382	10,699	5,683	1.88	1.04	1.80 (1.77-1.83)
CEI 6 months	22,256	15,469	6,787	2.28	1.10	2.07 (2.04-2.10)
No blackout period^b	20,959	15,478	5,481	2.82	1.12	2.52 (2.49-2.55)

CEI continued exposure interval, cSR crude sequence ratio, SRnull null-effect sequence ratio, aSR adjusted sequence ratio, 95% CI 95% confidence interval
^aThe assumptions of the parameters used in the primary analysis were: washout window 12 months, exposure window 12 months, CEI 4 months and blackout period 7 days
^bPatients are excluded if they have their first prescription of the index and marker medication on the same date, as the sequence of the index and marker medication cannot be determined

ISSN: 1471-2288