Abstract
Objective To determine how duration of observation affects estimation of incidence and prevalence of systemic lupus erythematosus (SLE).
Methods SLE incidence and prevalence estimates from data periods as brief as 3 years (2001-2003) were compared to estimates from a 15-year period (1989-2003).
Results The 15-year period incidence was 5.6/100,000 (95% CI 5.0–6.1) and the prevalence was 59.1/100,000 (95% CI 57.4–60.8). When a 3-year period was used, incidence was overestimated by 238.1% and prevalence underestimated by 66.0%.
Conclusion SLE incidence and prevalence estimates vary considerably according to the observation period; more than 5 years of data is likely required.