1. What is the differences between comparative (age-standardized) and national (crude) prevalence, and when to use which?
The national (crude) prevalence is the percentage of each country's population that has diabetes. It is appropriate for assessing the burden of diabetes for each country.
The comparative prevalence has been calculated by assuming that every country and region has the same age profile (the age profile of the world population has been used). This reduces the effect of age differences between countries and regions, and this figure is appropriate for making comparisons between. The comparative prevalence should not be used for a single country or region who have diabetes.
Please download the summary table in excel format in the Download section.
To understand where the prevalence estimates come from and how they are calculated please refer to the Methodology described in the Appendix (p 89-99) of the following background paper: Diabetes and Impaired Glucose Tolerance. To see which studies were used for each country please also refer to the Data Sources tables in the background paper (Africa: Table 11, page 37; Europe: Table 16, page 47; Middle East and North Africa: Table 21, page 54; North America and Caribbean: Table 26, page 59; South and Central America: Table 31, page 64; South-East Asia: Table 36, page 69; Western Pacific: Table 41, page 78).
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For most low income countries few people with type 1 diabetes survive long in adulthood so it is close to 0%. In higher income countries around 5% to 10% have type 1 diabetes and the rest type 2 diabetes. To better understand why data about type 1 diabetes is only available for the young (and not for the adult population), please refer the following background paper (p3): Diabetes in the Young.
Because this is the age group covered by most studies. For most countries there is little or no prevalence information about people with diabetes below 20 or above 80 years. Prevalence studies usually only include ages within this range, and often the upper age group is open-ended, for example, 65+.
7. Are the IGT figures in the IDF Diabetes Atlas comparable to 'pre-diabetic' figures? They seem low compared to other figures.
"Pre-diabetes" refers to a combination of IGT and IFG, so the IGT figures alone will necessarily be lower than estimates of "pre-diabetes".
The editor of the IDF Diabetes Atlas is the International Diabetes Federation. For more details about the contributors and the editorial team please refer to the Acknowledgements page.
9. Why are some countries with a very high diabetes prevalence estimates not included in the World Top 10 Diabetes prevalence table? (Table 2.1)
The World Top 10 table only includes countries where surveys with glucose testing have been carried out (as noted in the footnote). This means that some countries with very high diabetes prevalence estimates are not included because no such survey has been undertaken in the country. When no survey has been conducted in a country we extrapolated from the data of another country.
10. Where I can I find prevalence estimates for type 2 diabetes? I can see the estimates for all diabetes but not for type 2.
The prevalence estimates are for all people with diabetes aged 20-79 years. Most prevalence studies publish data on total diabetes and do not separate by type of diabetes, therefore we are not able to determine the prevalences separately.
In most countries, around 90% of people with diabetes have type 2 diabetes, although it varies by country. In poorer countries the life expectancy for people with type 1 is shorter, and the incidence may be lower, therefore the proportion of adults with type 2 diabetes is usually higher than 90%. Refer to question #5 to understand why do we not have data about type 1 diabetes in the adult population.
In order to correctly cite the Diabetes Atlas 4th edition, whether from its hard-copy or web version, you should refer to it the following way: "International Diabetes Federation. IDF Diabetes Atlas, 4th edn. Brussels, Belgium: International Diabetes Federation, 2009."