Despite the fact that the false-positive and false-negative rates in this study were higher than reported in previous studies (19, 23), the net effect of disagreement between UCOD codes on reported mortality rates for endogenous and exogenous UCODs was not significant.
Therefore, efforts to improve mortality statistics in Hermosillo should include analysis of the reliability of the UCOD codification process.
These study results suggest that strengthening educational interventions targeted at medical students and introducing automated tools in the UCOD coding process may improve the quality of the Sonora death certification system.
The codes for the original UCODs were based on the three-digit category of the International Classification of Diseases, 10th Revision (ICD-10).
Both the original and new UCODs were classified into two categories: endogenous causes (including neoplasms; blood diseases; endocrine, nutritional, and metabolic diseases; certain conditions originating in the perinatal period; and congenital malformations, deformations, and chromosomal abnormalities), and exogenous causes (including respiratory infections, infectious and parasitic diseases, and accidents and other external CODs) (18).
The original UCODs (those from the 2002-2003 death certificates) were then compared to the new UCODs (those determined by the expert reviewers) to measure concordance between the two sets of data, with the new UCODs used as the "gold standard" for all subsequent analyses.
To evaluate the effect of inaccurately completed COD statements on infant mortality statistics, age-adjusted mortality rates were estimated using the new UCODs and compared with the original estimated age-adjusted rates (those based on the original UCODs).
The age-adjusted mortality rates, based on the original UCODs (those assigned by the original death certifier) and the new UCODs, and the resulting MRRs (the ratios of the original age-adjusted mortality rates to those based on the new UCODs) for the main groups of causes of perinatal and post-neonatal deaths are displayed in Table 4.
Because these COD statements are entered into the SEED database, and Sonora infant mortality statistics are derived from the SEED data, the results of this study suggest systematic inaccuracies may be causing underestimation of infectious and parasitic diseases and overestimation of conditions originating in the perinatal period, neoplasms, blood diseases, and endocrine and metabolic diseases as UCODs among infants.
Analysis of the accuracy of the COD statements indicated discordance between almost 50% of the original UCODs and those assigned by the expert reviewer.