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Fig. 4 | BMC Infectious Diseases

Fig. 4

From: Sample size considerations using mathematical models: an example with Chlamydia trachomatis infection and its sequelae pelvic inflammatory disease

Fig. 4

Relative risk and sample size per group varying duration of infection and fraction developing PID. The contour plots present the estimated relative risk (RR) and the corresponding sample size needed per group for the constant progression (Panel a and c) and for the progression at the end (Panel b and d) while varying infection duration and fraction of women developing PID. The contour lines show for which combinations the RR and the sample size remain the same. For all other model parameters the baseline values were used (TableĀ 1, Generic sample size calculation). Note that the RR and sample size needed per group cannot be estimated if the fraction of women who develop PID equals the prevalence and progression to PID is constant because this results in a division by zero in the RR formula (indicated by the grey area in (a) and (c))

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