The quality of mortality statistics of causes of death has increased throughout the 40 years studied in Spain in women and men. However, quality gaps still remain across regions. Meanwhile, the best regional quality results have showed that there is scope for targeted upgrade.
In our experience, two major components comprise reliable quality of CoD statistics: one component involves medical certification (professionalism, health record access, and healthcare administration type) and the other involves post-certification and related to mortality registers [32, 33], coding skills [34], and the capacity for documental health information recovery [12].
Our purpose was the internal comparison of the regions with Spain over a long period. The age-standardised rates to the European Standard Population fulfilled our purpose of national and international comparison. However, given the general decrease in the quality of mortality categories, we chose to describe its proportion with respect to all-cause of death between periods, thus giving a better description. At the same time, the comparative mortality ratios made it possible to test, by internal comparison, in a stable way across all the regions in a long period.
This study has some limitations. The CoD selection and quality grouping may lack of comparability. However, our consensus on ICD10 code selection was based on the ICD10 instructions manual [35] and literature revision [6, 12, 36]. The two major proposals of quality assessment of CoD come from the Centers for Disease Control [6] and Anaconda software® [36], but these showed some qualitative differences. The CDC paper established 3 subtypes of UCoD (unknown & ill-defined, immediate & intermediate, and nonspecific). The unknown and ill-defined causes included fewer codes than the ICD10 (18th chapter and annex 7.3). These immediate or intermediate UCoD could also be reassigned to a general unspecific group, as well as to the ill-defined group by WHO criteria (ICD10 code I50 for heart failure). The annual national summary of 2.2% for unknown and ill-defined causes versus a 32.5% for the other unsuitable CoD, seems a broad gap to take action (Supplementary Annex B) [6, 12]. The Anaconda software encompasses 3 axes: the 1st axe, five qualify for uninformative subtypes (1- symptoms, sign, and ill-defined conditions; 2- impossible as UCoD; 3- intermediate CoD; 4- immediate CoD; and 5- insufficiently specified CoD extracted from Global Burden Disease (GBD) [37]; the 2nd axe, four levels of health impact policies of 800 codes (Supplementary Annex B); and the 3rd axe, a vital performance index (of completeness, and garbage and impossible codes by age and sex). Although, GBD is dynamically updated [38], this praiseworthy effort, also expresses complex assessment outcomes, to take action further than lack of completeness [28, 39] and high numbers for ill-defined CoD, especially in low-income countries [10, 18]. In our case, for example, we considered dementia, ictus, pneumonia, or accidental poisoning by narcotics, reliable as primary health care diagnostics, however a detailed hospital-like testing technology may improve their accuracy.
The health and judicial administration framework matters in medical certification. Spain is supported by a Welfare State with National Health and Social Systems (public funding, universal access, a majority of centres of governmental propriety, and regional competences in health and social care budget and management), as well as a judicial system with forensic pathology and laboratory facilities at every regional centre. The Western European context of public funding and universal health care provision (private versus governmental) could be associated with completeness and validity of causes of death [40]. Likewise, the majority of diseases can be diagnosed through anamnesis and conventional physical examination and complementary tests at the Primary Health Care subsystem.
The process of completing and accurately coding a death certificate according to the ICD is challenging for all countries. Not all of them have achieved a good-quality threshold on mortality data. The WHO included in the medium-quality category several high-income Western European countries (such as Austria, Belgium, Denmark, France and Germany, regulated by universal Health Insurance systems) [14, 41]. Furthermore, in the present decade six high-income countries worldwide achieved a 9–31%, adding ill-defined (ICD10, 18th chapter) to impossible UCoD [19]. Similarly, it would be a specificity error to classify 67.3% of the vital registration deaths as least-specific codes, without any further geographical or social context reference [22]. Providing the magnitude of poor quality death certification, health authorities did not seem to play a role in the probable random underestimation of the great and leading CoD [7, 13, 27–29, 32]. Currently, the COVID-19 pandemic has probably worsened death certification [42]. Statistics and health authorities may consider implementing the framework conditions to avoid miscertification. In addition, the WHO may include ill-defined conditions in the same ICD chapter in future revisions. Meanwhile, some national CoD registries have achieved top quality [33], and could be a standard target to replicate.
Some papers have emphasised the weakness of imputations made by case identification algorithms based on available health and population record information. The imputations from multiple search assignments of unsuitable CoD were proportionally predicted [11, 13, 19–22, 43, 44] without a representative sample of validation [7, 13, 28, 29, 32].
This study showed that a lower pattern was a proxy for regional inequality, affecting Southern regions of Spain, which also have lower Gross Domestic Products (Fig. 1, please see the left map area of the Northwest-Southeast economic diagonal of Spain). Moreover, poor death certification may be linked to individual characteristics (such as medical professionalism, the social stratum of the deceased, etc.) [45, 46]. This misclassification would imply regional and individual differential errors. The long-time evidence of our results is suggestive of a new organisational model with a multilevel health experts support to the National Institute of Statistics for a better regional and national standards upgraded [34].
Some studies have associated the deficiency of medical specialist education on death certification with miscertification in mortality statistics [47]. Courses for the improvement of CoD notification have oftentimes been imparted with diverse approaches and to different alumni, such as medical students or physicians in their specialisation [43, 48, 49]. Nowadays, this training is available through new communication technologies such as mobile phones [44], websites and e-learning platforms [43, 50]. Additionally, the WHO may introduce a certification of “medical competence on certification of causes of death” to foster the quality of mortality statistics worldwide.
As stated before, there is a general need of representative national validity studies of causes of death to address properly the post-certification informatics reassignment in CoD.