Impact of ONS Population Projection Changes on Dementia Diagnosis Rates

Impact of ONS Population Projection Changes on Dementia Diagnosis Rates

Calculation of dementia diagnosis rates

The dementia diagnosis rate (DDR)for a CCG is calculated as the number of people aged over 65 with dementiaon their GP registersdivided by the expected dementia population for that CCG(1). This expected dementia population can only be an estimateand comes from a combination of information from the Cognitive Function and Ageing Study II (CFAS II) study(2)and the Office of National Statistics (ONS) population projection for that financial year(3), which is another estimate.

The required standard is a DDR of 66.7%.

From April 2016 (data reported in May), the ONS figures changed to use 2016/17 rather than 2015/16 population estimates. This saw an increase in the estimated target population (Over 65s) which consequently, as this figure contributes to the denominator in the diagnosis rate calculation, resulted in a decrease in the diagnosis rate for the majority of CCGs.

Where the actual number of patients on the dementia register was relatively static, the DDR fell. Those CCGs who had made efforts to increase the numbers diagnosed from March to April 2016 may have seen their DDR increase less than expected, stagnate, or fall due to the change in the denominator of the calculation.

The following tables show six months’ data including April 2016 which uses the revised denominator. The table also includes the percentage population increase from ONS figures – this indicates those CCGs with the largest population changes that may see the greatest impact on the DDR.

Most notably England has fallen 1.1 percentage points from 67.5% (meeting the standard) to 66.4% (failing the standard).

References:
(1)
(2)
(3)As provided by the Office of National Statistics to NHS England Analytical Services

Table 1
DDR for North RegionDCOs (November 2015 – April 2016)

The above table shows six months’ data including April 2016 which uses the revised denominator. The table also includes the percentage population includes from ONS figures – this indicates for those CCGs with the largest population changes may see the greatest impact on the DDR. You will note that delivery against the standard has decreased at each DCO aggregate level.

Table 2
DDR for North RegionCCGs (November 2015 – April 2016)

The above table shows six months’ data including April 2016 which uses the revised denominator. The table also includes the percentage population increase from ONS figures – this indicates those CCGs with the largest population changes that may see the greatest impact on the DDR.

For all but seven CCGs in the North, the DDR has fallen between 0.2 and 5.3 percentage points (highlighted red); some to the extent of failing the standard where previously this was met.

In order to assess the continuing trajectory of CCGs in the North region for April, the diagnosis rate was recalculated using the previous 2015/16 population figures.
The following is a summary for the North region of the DDR for March 16 (using 15/16 ONS data), April 16 (using 16/17 ONS data), and April 16 (using 15/16 ONS data). The column ‘CHANGE’ indicates the differences between the March 16 (using 15/16 ONS data) and April 16 (using 15/16 ONS data), enabling us to assess the change in DDR while essentially ignoring the change to the denominator (see column Apr 15/16 below).

Table 3: Impact of Population Change on Dementia Diagnosis Rates, North of England DCOs

The column ‘CHANGE’ indicates the differences between the March 16 (using 15/16 ONS data) and April 16 (using 15/16 ONS data), enabling us to assess the change in DDR while essentially ignoring the change to the denominator (see column Apr-16 with 15/16 prevalence).

Table 4: Impact of Population Change on Dementia Diagnosis Rates, North of England CCGs