Impact on total population health and societal cost, and the implication on the actual cost-effectiveness of including tumour necrosis factor-α antagonists in management of ankylosing spondylitis: a dynamic population modelling study

Table 2 Types and parameter estimates of the distributions of the patient characteristics in the prevalent population on January 1, 1996 and in each yearly incident cohort

Characteristics	Distribution^a
	Prevalent population (PP) Estimated size: 62,000 patients	Yearly incident cohort Estimated size: 1000–1200 patients
Age of male	N (42.5, 12.6)	N (33.7, 8.14)
Age of female	N (46.3, 12.7)	N (33.7, 8.14)
Gender (male)	Bern (0.69)	Same as PP
Symptom duration	N (0.64 × Age − 7.76, 1.20 × \(\sqrt {Age}\))^b	Same as PP
Diagnosis duration	N (3.1, 1.3)^c	0
Proportion of patients with paid jobs	Bern (0.75)	Same as PP
Proportion of paid-job patients being work disabled	Bern (0.20)	Same as PP
Contraindication to anti-TNF agents	Bern (0.20)	Same as PP
BASDAI	N (1.72, 0.63)^c	N (1.91, 0.52)^c
BASFI of male patient	N (0.69 × BASDAI + 1.89, 1.69)^d	N (0.60 × BASDAI + 2.62, 1.42)^d
BASFI of female patient	N (0.92 × BASDAI + 0.19, 1.00)^d	N (0.91 × BASDAI + 0.27, 0.81)^d

BASDAI Bath Ankylosing Spondylitis Disease Activity Index, BASFI Bath Ankylosing Spondylitis Functional Index
^aN (m, s): Normal distribution with mean m and standard deviation s; Bern (p): Bernoulli distribution with probability of true value being p
^bDistribution conditional on age; parameters estimated by fitting a linear model using generalized least squares with fixed variance weights
^cDistribution of square root of the respective characteristics
^dDistribution conditional on BASDAI

ISSN: 1478-7547