4. Prevalence

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We use basic proportions to calculate the prevalence of functional difficulties in each country based on the A categorization above for all data sets and based on the B and C categorizations for countries with a graded answer scale. Prevalence rates for a country reflect the country’s own population structure and are not adjusted for age and sex.

The prevalence rates at the individual and household (HH) levels are calculated using the formulas:
\[\text{Prevalence Rate}_c = {\text{Number of adults with functional difficulty}_c \over \text{Total Population}_c.}\]

where c denotes a country.

\[\text{HH Prevalence Rate}_c = {\text{Number of households with at least one adult with functional difficulty}_c \over \text{Number of households}_c.}\]

The difference between the individual and the household level prevalence rates depends on household size and the extent to which there might me more than one adult with functional difficulty in a household.