Open Access Study protocol

Methods for economic evaluation of a factorial-design cluster randomised controlled trial of a nutrition supplement and an exercise programme among healthy older people living in Santiago, Chile: the CENEX study

Damian G Walker1*, Cristian Aedo2, Cecilia Albala3, Elizabeth Allen4, Alan D Dangour5, Diana Elbourne4, Emily Grundy6 and Ricardo Uauy5

Author Affiliations

1 Department of International Health, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, USA

2 Human Development Department, Latin America and the Caribbean Region, The World Bank, 1818 H Street, NW Washington, DC 20433, USA

3 Instituto de Nutrición y Tecnología de los Alimentos (INTA), University of Chile, Santiago, Chile

4 Medical Statistics Unit, Department of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine (LSHTM), London, UK

5 Nutrition and Public Health Intervention Research Unit, Department of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, UK

6 Centre for Population Studies, Department of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, UK

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BMC Health Services Research 2009, 9:85  doi:10.1186/1472-6963-9-85

Published: 27 May 2009



In an effort to promote healthy ageing and preserve health and function, the government of Chile has formulated a package of actions into the Programme for Complementary Food in Older People (Programa de Alimentación Complementaria para el Adulto Mayor - PACAM). The CENEX study was designed to evaluate the impact, cost and cost-effectiveness of the PACAM and a specially designed exercise programme on pneumonia incidence, walking capacity and body mass index in healthy older people living in low- to medium-socio-economic status areas of Santiago. The purpose of this paper is to describe in detail the methods that will be used to estimate the incremental costs and cost-effectiveness of the interventions.

Methods and design

The base-case analysis will adopt a societal perspective, including the direct medical and non-medical costs borne by the government and patients. The cost of the interventions will be calculated by the ingredients approach, in which the total quantities of goods and services actually employed in applying the interventions will be estimated, and multiplied by their respective unit prices. Relevant information on costs of interventions will be obtained mainly from administrative records. The costs borne by patients will be collected via exit and telephone interviews. An annual discount rate of 8% will be used, consistent with the rate recommended by the Government of Chile. All costs will be converted from Chilean Peso to US dollars with the 2007 average period exchange rate of US$1 = 522.37 Chilean Peso. To test the robustness of model results, we will vary the assumptions over a plausible range in sensitivity analyses.


The protocol described here indicates our intent to conduct an economic evaluation alongside the CENEX study. It provides a detailed and transparent statement of planned data collection methods and analyses.

Trial registration