Open Access Open Badges Research article

Does the pharmacy expenditure of patients always correspond with their morbidity burden? Exploring new approaches in the interpretation of pharmacy expenditure

Amaia Calderón-Larrañaga1*, Beatriz Poblador-Plou1, Anselmo López-Cabañas1, José Tomás Alcalá-Nalvaiz2, José María Abad-Díez13, Daniel Bordonaba-Bosque1 and Alexandra Prados-Torres1

Author Affiliations

1 Aragon Health Sciences Institute (I + CS), Zaragoza, Spain

2 Department of Statistical Methods, Science Faculty, University of Zaragoza, Zaragoza, Spain

3 Department of Health and Consumer Affairs, D.G. Planning and Assurance, Government of Aragon, Zaragoza, Spain

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BMC Public Health 2010, 10:244  doi:10.1186/1471-2458-10-244

Published: 11 May 2010



The computerisation of primary health care (PHC) records offers the opportunity to focus on pharmacy expenditure from the perspective of the morbidity of individuals. The objective of the present study was to analyse the behaviour of pharmacy expenditure within different morbidity groups. We paid special attention to the identification of individuals who had higher values of pharmacy expenditure than their morbidity would otherwise suggest (i.e. outliers).


Observational study consisting of 75,574 patients seen at PHC centres in Zaragoza, Spain, at least once in 2005. Demographic and disease variables were analysed (ACG® 8.1), together with a response variable that we termed 'total pharmacy expenditure per patient'. Outlier patients were identified based on boxplot methods, adjusted boxplot for asymmetric distributions, and by analysing standardised residuals of tobit regression models.


The pharmacy expenditure of up to 7% of attendees in the studied PHC centres during one year exceeded expectations given their morbidity burden. This group of patients was responsible for up to 24% of the total annual pharmacy expenditure. There was a significantly higher number of outlier patients within the low-morbidity band which matched up with the higher variation coefficient observed in this group (3.2 vs. 2.0 and 1.3 in the moderate- and high-morbidity bands, respectively).


With appropriate validation, the methodologies of the present study could be incorporated in the routine monitoring of the prescribing profile of general practitioners. This could not only enable evaluation of their performance, but also target groups of outlier patients and foster analyses of the causes of unusually high pharmacy expenditures among them. This interpretation of pharmacy expenditure gives new clues for the efficiency in utilisation of healthcare resources, and could be complementary to management interventions focused on individuals with a high morbidity burden.