Table 1 Sources of variation in estimating the national prevalence of muscular dystrophies
Source of Variation | Identified from | |
|---|---|---|
In All Surveillance | Literature | Survey |
Unidentified or unavailable data sources | x | x |
Unidentified cases at known data sources | x | |
Misclassified disease status | x | |
Migration into and out of surveillance system | x | |
Time period for case capture | x | x |
Time between diagnosis and ascertainment | x | |
Regional differences in disease incidence | x | |
Unreliable, non-specific coding in screening databases | x | x |
Migration into and out of surveillance region | x | x |
Demographic changes due to rapid population change | x | x |
Specific to Rare Disease Surveillance | ||
Unstable estimates due to small number of cases | x | |
Misclassification of muscular dystrophy type | x | x |
Specific to Medical Records-Based Surveillance | ||
Lack of standardized data in medical records | x | |
Underreported and incomplete data in medical records | x | x |
Number and proportion of treatment centers within the study area | x | |
Specific to Extrapolation to National Estimates | ||
Differences between study population and national population | x | |
Differential ascertainment between areas or groups of patients | x |