Study of social loss or gain from a particular cause: scope for the developing countries - a review with reference to cancer.

Incidence rates have long been used to assess the burden of different diseases in a population, whereas loss due to occurrence of diseases is studied using the death rates. Death rates however, are based on and therefore describe, only number of lives lost. There have been two approaches to arrive at the actual loss or gain from a particular cause viz. Person years of life lost (PYLL) approach and cause elimination life table (CELT) approach. This review covers these approaches and the competing risk theory and models focusing on the methodological developments. A summary of the conceptual and methodological developments on these concepts has also been presented. There are eight possible approaches in dealing with the loss in the presence or gain in the absence of a particular cause of death depending upon the preferences related to PYLL/CELT approach, modeling/descriptive approach, considering or without considering competing causes. A close look at the two basic approaches reveals that PYLL and cause elimination are just different terminologies used to address the same quantity, loss in the presence or gain in the absence. As far as descriptive vs. modeling approaches are concerned, all the descriptive procedures can be put in the form of models and all the models can be presented in a descriptive way. Regarding results using different models, no practical difference exists in the results based on different models for competing risks. However, exclusion of the competing risks may result in a considerable bias in the developing countries where general mortality is relatively higher. This review study suggests freedom in the selection of a modeling or a descriptive approach without any considerable loss of accuracy but at the same time emphasizes the consideration of the competing risks. An empirical study may be recommended to confirm the conclusions of this study.

An indirect study of cancer survival in the context of developing countries.

With classical approaches, survival refers to the life of a person after diagnosis of disease, and survival studies deal with measurement of the same to evaluate overall performance of a group of patients in terms of quality and quantity of life after diagnosis/treatment. There are numerous difficulties in the conduct of a population-based survival study in the context of developing countries, including India. Loss to follow-up is a typical problem encountered, causing biased estimates. In view of this difficulty with the classical approach, the objective of this study was to propose an indirect methodology for the study of survival. The proposed methodology is based on life table techniques and uses current data on incidence and mortality from the disease. It involves the estimation of person years free of disease (PYFD), person years with disease (PYWD), person years of life lost (PYLL) and average duration of disease (ADD) and their comparison over a time period. Empirical application was carried out for mouth and lung cancers in males and cancers of breast and cervix in females as well as for all sites combined together in each sex. Cancer incidence and mortality data by age and sex for the years 1989, 1993, 1997 and 2001 were obtained from published reports of Mumbai Cancer Registry, India. All causes of deaths for these years were obtained from Mumbai Municipal Corporation. Three life tables were constructed by applying various attrition factors: (a) risk of death from all causes; (b) risk of incidence and that of death from other causes; and (c) risk of death from other causes only. The expectation of life from the second life table gave PYFD. PYWD and PYLL were calculated by suitable subtractions among three expectations of life. ADD was calculated by dividing person years lived with disease by number developing the disease. It was noted that during 1993-2001, PYFD for all sites increased from 59.4 to 62.1 and from 63.8 to 66 years in males and females respectively. PYLL was about 0.8 year in males and 1 year in females. Similarly, PYWD was 0.6 and 1 year in males and females. ADD for all sites varied from 4 to 4.7 years in both sexes. It was about 6 years for mouth cancers and 2 years for lung cancers in males and 4-5 years for breast and cervical cancers in females. Validation of the ADD was carried out by comparison with published data for calculating median duration of disease. Given the difficulties in conduct of classical survival studies, the proposed method may provide a useful tool for having a regular audit of prognostic factors in the community.