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Table 1 Parameter values describing the natural history of chlamydia infection, PID development and the screening intervention

From: Timing of progression from Chlamydia trachomatisinfection to pelvic inflammatory disease: a mathematical modelling study

Parameters Baseline values Explanation Sensitivity analysis Source
    Distribution Parameters  
Model parameters
λ   Force of infection (per day), calculated using*     
1/r 365 Mean duration of infection (days) [6, 16] N(μ,σ2) μ=365 σ2=752 Consensus
p 5.7% Prevalence at baseline [11] Bin(n,p) n=2519 p = 143 2519 [11]
α   Effective testing rate (per day), calculated using     
c 22.2% Coverage of testing uptake (per year) [11] Bin(n,p) n=2377 p = 527 2377 [11]
δ 8.0% Treatment failure [17] U(a,b) a=0% b=50% Consensus
f estimated Fraction of women becoming infected with chlamydia who will develop PID     
Input parameter
x 30.0% Proportion of PID cases due to chlamydia in control group [11] Bin(n,p) n=23 p = 7 23 [11]
  1. *In the absence of the tria (α=0), to observe chlamydia prevalence p at steady state: λ = p 1 p r .
  2. Reported uptake of chlamydia testing c during the follow-up period (outside of the trial) is reduced by the proportion with treatment failure δ, which results in the effective testing rate α = l n 1 1 δ c 365 per day [18].
  3. N(μ,σ2), normal distribution (mean, variance); Bin(n,p), binomial distribution (size, probability); U(a,b), uniform distribution (minimum, maximum).