The future excess fraction model for calculating burden of disease

Our plain-English summary of The future excess fraction model for calculating burden of disease, by L. Fritschi, J. Chan, S.J. Hutchings, et al (BMC Public Health, 2016).

The study

• Authors: L. Fritschi, J. Chan, S.J. Hutchings, T.R. Driscoll, A.Y. Wong, R.N. Carey
• Journal: BMC Public Health
• Published: 2016;16:386
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Estimates of the burden of disease caused by a particular agent are used to assist in making policy and prioritizing actions. Most estimations have employed the attributable fraction approach, which estimates the proportion of disease cases or deaths in a specific year which are attributable to past exposure to a particular agent. While this approach has proven extremely useful in quantifying health effects, it requires historical data on exposures which are not always available.

Methods: We present an alternative method, the future excess fraction method, which is based on the lifetime risk approach, and which requires current rather than historical exposure data. This method estimates the future number of exposure-related disease cases or deaths occurring in the subgroup of the population who were exposed to the particular agent in a specific year. We explain this method and use publically-available data on current asbestos exposure and mesothelioma incidence to demonstrate the use of the method.

Conclusions: Our approach to modelling burden of disease is useful when there are no historical measures of exposure and where future disease rates can be projected on person years at risk.

In plain English

This methods paper presented a new burden-of-disease method, the future excess fraction method. It needs exposure data for one current year rather than historical data, and estimates future exposure-related cases or deaths among people exposed that year. The authors demonstrated it with occupational asbestos exposure and mesothelioma in Australia's 2012 working-age population (18–65 years). They used a relative risk from a Spanish study and projected mesothelioma rates to 2094. They estimated that 253 110 men and 2757 women were occupationally exposed in 2012. They put lifetime mesothelioma risk at 33/10 000 for males and 15/10 000 for females. They estimated 7549 future mesotheliomas in men and 22 in women due to 2012 exposure, about 32% of future male cases and under 1% of female cases. Results were sensitive to the number exposed, population numbers and the relative risk. Projecting over 80 years makes large errors likely, the authors noted. They added that, for exposures that change over time such as occupational ones, counting only one year's exposure will underestimate future cases. The authors concluded that the method expresses disease burden in a readily understandable way.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Methods paper (technical advance) describing a new calculation method, the future excess fraction method, based on the lifetime risk approach. It is illustrated with a modelling example that uses publicly available Australian data.
• Who was studied: A 'virtual cohort' made up of Australia's 2012 working-age population (18–65 years), stratified by sex, followed in projections from 2012 to 2094.
• Exposure: Occupational exposure to asbestos in 2012, recorded only as exposed or not exposed in that year. Fiber type is not specified. The relative risk of mesothelioma for occupationally exposed people was taken from a Spanish study; the article does not print its value.
• Main results:
  • An estimated 253 110 working-age males and 2757 working-age females were occupationally exposed to asbestos in 2012 (proportions 0.0347 and 0.0004).
  • Lifetime risk of mesothelioma in the 2012 working-age population was estimated at 33/10 000 for males and 15/10 000 for females.
  • Total mesotheliomas projected in the 2012 working-age population until 2094: 23,819 in males and 10,679 in females.
  • Lifetime excess risk of mesothelioma for those exposed to asbestos in 2012: 4.26% for males and 3.34% for females.
  • Future number of mesotheliomas due to occupational asbestos exposure in 2012: 7549 in males and 22 in females.
  • About 32% of future mesotheliomas in males (fraction 0.317) and under 1% in females (fraction 0.002) in the 2012 working-age population were estimated to be due to occupational exposure among those exposed in 2012.
  • For comparison, the attributable fraction method gave an estimated 240 mesotheliomas in men in the year 2052 due to exposure in 2012 (attributable fraction 39%). For women it gave 1 mesothelioma (attributable fraction under 1%).
  • In sensitivity analysis, the estimates were sensitive to the prevalence of exposure, population numbers and relative risks, but much less sensitive to changes in mortality.
• The authors' conclusion: The authors concluded that the future excess fraction method offers a different way of expressing the burden of disease that is readily understandable by the general public and by decision-makers.
• Limitations the authors state:
  • Disease rates were projected more than 80 years into the future, so errors are likely to be large.
  • The projection tool (CanProj) bases future trends on past observations and does not account for possible changes in risk factors.
  • For exposures that change over time, such as occupational exposures, using exposure in the index year only (point prevalence) rather than 'ever exposed' will underestimate the number of future cases. The authors say this may not apply to relatively constant exposures such as obesity and alcohol intake.
  • There was no information on how long exposure had lasted or how intense it was.
  • No latency period was included in the lifetime risk estimates. The authors argued that this was not needed for a lifetime approach.
  • The future excess fraction is not directly comparable with the attributable fraction, because the two estimate different concepts using different data.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Mesothelioma.

Related studies

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• Determinants of malignant pleural mesothelioma survival and burden of disease in France: a national cohort analysis — C. Chouaid, J.B. Assié, et al. (2018)
• An approach to estimating the environmental burden of cancer from known and probable carcinogens: application to Ontario, Canada — S.L. Greco, E. MacIntyre, et al. (2020)
• Treatment patterns and humanistic burden of malignant pleural mesothelioma in Spain — S. Cedres, J. Calvete, et al. (2025)
• Assessment of the future mesothelioma disease burden from past exposure to asbestos in ship recycling yards in India — R. Singh, J.W. Cherrie, et al. (2020)
• Investigation of the trends and associated factors of ovarian cancer in Indonesia: A systematic analysis of the Global Burden of Disease study 1990-2021 — B.A. Tjokroprawiro, K. Novitasari, et al. (2025)

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