Estimates of dementia prevalence in spite of the lack of consistent data are made on the basis of the number of case studies.

By dementia prevalence we mean the number of patients suffering from dementia and their percentage in the total population at a particular time.

Throughout the world dementia surveys are being carried out all of which yield slightly different results as the surveys are carried out using varying methods and procedures.

However the common conclusion of all these surveys is the same - dementia cases are registering an alarming rise, especially with age.

These figures were collected from Japan, Australasia, North America and Europe and other such developed countries and are not universal.

Contradictory views prevail with regard to dementia prevalence in extreme old age. One school of medical experts believes that if people live for a really long time, then all of them will develop dementia.

The other school is of the opinion that dementia risk is leveled out at extreme old age and there may be a drop in the occurrence percentage by 0.3 in such an age.

There is no noticeable difference between the sexes when it comes to dementia prevalence but very old women are at a slightly higher risk.

Of dementia, Alzheimer's is commonly seen in Caucasian races.

There is a wide prevalence of vascular dementia in former USSR, Japan.

Dementia is more commonly reported from developing countries like India (Kerala) and China than from developed nations.

There is also a very strong link between urbanity and dementia while rural populations are at lesser risk.

7.4 million People suffer from dementia in developed countries according to UN in 1990.