Mechanisms and mediation in survival analysis: towards an integrated analytical framework

Table 1 Variables included in the model (N = 5178)

Variable	Value	Summary data
Stage at diagnosis (three dummy variables)
	Stage I (reference)	559 (10.8 %)
	Stage II	1,812 (35.0 %)
	Stage III	1,678 (32.4 %)
	Stage IV	1,129 (21.8 %)
Treatment optimality (binary)^a
	sub-optimal (0)	995 (19.2 %)
	optimal/more aggressive (1)	4183 (80.8 %)
Age at diagnosis (continuous measure)	(Scaling factor = 0.10)
	< 60	1,109 (21.4 %)
	60–69	1,396 (27.0 %)
	70–79	1,779 (34.4 %)
	80+	894 (17.3 %)
Deprivation score (continuous)^b	(rescaled to 0–1 metric)
	Mean	0.58
	Standard deviation	0.13
Emergency admission (binary)^c
	First admission elective (0)	4,026 (77.8 %)
	First admission via A&E (1)	1152 (22.2 %)
High caseload hospital (binary)^d
	Less than or equal to 40 per annum (0)	2,876 (55.5 %)
	More than 40 per annum (1)	2,302 (44.5 %)

^aMissing values (4.4 %) were assigned to the modal category (optimal or more aggressive)
^bMissing values (< 1 %) were estimated using the EM algorithm in IBM SPSS Statistics v.20
^cMissing values (6.5 %) were assigned to the modal category (elective admission)
^dMissing values (< 1 %) for caseload were replaced using the caseload of hospital where first (rather than main) treatment was received or, if this was not possible, estimated using the EM algorithm in IBM SPSS Statistics v.20

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