|DATA SOURCES AND METHODS|
Mortality statistics are collected and made available by the WHO . Their advantages are national coverage and long-term availability, although not all datasets are of the same quality. For some countries, coverage of the population is incomplete, so that the mortality rates produced are implausibly low, and in others, the quality of cause of death information is poor. While almost all the Europen and American countries have comprehensive death registration systems, most African and Asian countries (including the populous countries of Nigeria, India and Indonesia) do not. For the GLOBOCAN 2008 estimates, we benefitted from the provisional estimates of the age- and sex-specific deaths from cancer (of all types) for 2008 in each country of the world. Prevalence data
1-, 3-, and 5-year prevalence is estimated from incidence estimates (for 2008) and observed survival by cancer and age group provided by cancer registries worldwide (see below). Prevalence is presented for the adult population only (ages 15 and over), and is available both as numbers and as proportions per 100,000 persons. Disability-adjusted life years (DALY)
A detailed description of the data sources and the methods of estimation used to obtain the parameters required to calculate DALYs have been described elsewhere . In brief, the following country- and cancer-specific sets of estimates were used in the computation of DALYs: (1) population data (source UN, see below), (2) incidence and mortality estimates from GLOBOCAN 2008, (3) estimates of the proportion cured and treated, (4) time intervals of distinct disease phases including duration of diagnosis and treatment, time to cure and to death, (5) standard life expectancy tables, and (6) disability weights. DALYs were estimated for each cancer site by sex and country. Population data
National population estimates for 2008 were extracted from the United Nation (UN) population division, the 2008 revision . The geographical definition of the regions follows the rules as defined by the UN (see the Population dictionary option). These estimates may differ slightly (especially for older age groups) from those prepared by national authorities.
The methods used to estimate the country specific burden of
cancer are similar to those used in the GLOBOCAN 2002 study  and have been
described in detail elsewhere . In summary, the most recent disease rates
available were applied to the corresponding population of the country in 2008.
For GLOBOCAN 2008, the degree of delay in the available data was taken into
account by computing predictions of the national incidence and mortality rates
to the year 2008, wherever possible. Although historical trends will not always
hold in the future, predictions based on relatively linear trend patterns have
been shown empirically to be reasonably accurate, particularly in the
short-term. Where the availability of annual data was minimal - commonly between 5 and 10
years - simple time-linear models were fitted to these data to predict
incidence and mortality for 2008 . Where data series spanning at least 15
years were available, predictions based on age-period-cohort modeling were
Estimates of cancer incidence by country
The methods to estimate the sex- and age-specific incidence rates of cancer for a specific country are dependant on the availability and the accuracy of data, and fall into one of the following categories, in priority order:
1. National Incidence data (62 countries)
2. Local incidence data and national
mortality data (52 countries)
(1) IN = MN * IR/MR
Before aggregation, each registry dataset was weighted
according to the square root of its population to take into account of the
relative size of the population covered. Depending on the accuracy and on the
availability of local data, one of two variants of the method was used:
|Estimates of the cancer mortality by country
National statistics are collated and made available by the WHO for countries with vital registration, but not all are of the same quality, and some corrections were made before they can be used for estimation purpose:
1. National Mortality data (65 countries).
2. Sample mortality data (31 countries).
3. No vital statistic available (88 countries).
3.1. We applied sets of cancer-, sex- and age-specific incidence to
mortality ratios provided by the national cancer registries in three Nordic countries
(Denmark, Finland and Norway) for the period 1953-1957  to the estimated
national incidence for 2008 (as a reciprocal of formula (1)).
(2) M = I [k-Sj ]
Where Sj is the relative survival at year j of follow-up and k is a
constant depending on j. When 5-year relative survival probabilities are used,
the constant k tends to be very close to unity.
Estimate of mortality from Kaposi sarcoma (KS) in sub-Saharan Africa
Estimates of cancer prevalence by country
The methods to estimate the sex age-specific prevalent cases by cancer for a
country have been described in detail . Partial prevalence (1-,3- and 5-year prevalent cases) were obtained by combining the estimated annual number of new cases and the corresponding probability of survival by time:
For example, one-year prevalence at a fixed point in mid-2008 was estimated from the number of new cases in 2008 multiplied by the probability of surviving at least six months. The above formula indicates that age was taken into account in both the incidence and survival data. The number of new cases for each country are those described and presented in GLOBOCAN 2008. The observed survival rates by age, sex, cancer and country at one and five years were obtained from various sources . One, three and five-year prevalence estimates are presented as the number or proportions of living patients by sex and country, for the same 27 cancer sites for which incidence is available.
Estimates of Disability-adjusted life years (DALYs)
DALYs are the sum of life years lost due to premature mortality (YLLs) and years lived with disability (YLDs). YLLs were calculated by multiplying the number of cancer-specific deaths at a given age group by the remaining life expectancy of a standard population for that age group. YLDs were computed by multiplying the number of incident cases at each non-fatal disease phase by the average duration of time associated with each disease phase. Disability weights were then multiplied by these life years to account for severity of each event. Finally, YLLs, YLDs and DALYs were converted into country-specific rates (per 100,000) by dividing the healthy life-years lost by corresponding population estimates. To allow cross-country and regional comparisons, rates were age standardised using the world standard population [15,16].
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