Calculating prevalence

For ease of comparison all of the prevalences on this site are based on the whole practice registered list, not just those in the correct age group - this applies to areas such as diabetes or epilepsy. This is largely because countries other than England do not list the specific number of patients on the practice list over, say, seventeen years old. It is also the prevalence that is used for adjustment of point value.
I was asked this week why the whole list is used for prevalence adjustment rather than the age adjusted subgroup. Is this unfair on practices? Well the answer is no, it is actually more fair the way it is, but for some quite complicated reasons. We have to look at some maths.
Point value = £ 160 × PracPrev AvgPrev × PracList AvgList Point value = £ 160 × ( Register PracList ) ( AvgReg AvgList ) × PracList AvgList Point value = £ 160 × Register PracList × AvgList AvgReg × PracList AvgList Point value = £ 160 × Register AvgReg Point value = £147 times {{PracPrev} over {AvgPrev}} times {{PracList} over {AvgList}} newline newline Point value = £160 times {{({Register} over {PracList})} over {({AvgReg} over {AvgList})}} times {{PracList} over {AvgList}} newline newline Point value = £160 times {{{Register} over overstrike{PracList}} times {overstrike{AvgList} over {AvgReg}}} times {overstrike{PracList} over overstrike{AvgList}} newline newline Point value= £160 times {{ Register } over { AvgReg }}

We have started from saying that the point value is modified by the practice prevalence relative to the average practice prevalence. Then the point value is modified by the relative size of the practice list overall. The second line expands this a bit by using the register size and the list size against the averages. It is true that this is not exactly how the average prevalence is calculated but it is pretty close.

After simplifying the formula there is a lot we can cancel from the top and bottom until we get to the final formula which basically says that the practice gets a set amount per person on the register but that this drops as the national average register size rises. Nothing else matters.

We can try again using an 'Eligible' denominator for the register.

Point value = £ 160 × PracPrev AvgPrev × PracList AvgList Point value = £ 160 × ( Register Eligible ) ( AvgReg AvgEgble ) × PracList AvgList Point value = £ 160 × Register Eligible × AvgEgble AvgReg × PracList AvgList Point value = £ 160 × AvgEgble Eligible × Register AvgReg × PracList AvgList Point value = £160 times {{PracPrev} over {AvgPrev}} times {{PracList} over {AvgList}} newline newline Point value = £160 times {{({Register} over {Eligible})} over {({AvgReg} over {AvgEgble})}} times {{PracList} over {AvgList}} newline newline Point value = £160 times {{{Register} over {Eligible}} times {{AvgEgble} over {AvgReg}}} times {{PracList} over {AvgList}} newline newline Point value = £160 times {{{AvgEgble} over {Eligible}} times {{Register} over {AvgReg}}} times {{PracList} over {AvgList}}

There is much the same process here but there is a lot less to cancel out. That is not necessarily a bad thing but we can see how this formula behaves. If we assume a practice of average list size then the last term will be one. If it has an average register size for diabetes then the middle term will be one as well. Interestingly in this case the point value would vary with the proportion of over 17 year olds on the practice list (i.e. Eligible would change without changing the overall list size). This is not what we want to see at all as the practice list makeup would alter income without any change to the actual number of patients treated.

So that is why the overall list size is used to calculate prevalence.

Release notes 2015

All four countries now have data on the site for the year 2014/15. The four countries have continued to diverge in their requirements and common ground is becoming smaller. Where indicators are broadly equivalent I have tried to make them comparable.

There are a couple of things worth noting below.


Wales was first to publish this year, about two weeks ahead of Scotland and a month ahead of England and Northern Ireland, which was impressive. There are no significant issues with their statistics. They have continued to publish data about local practices groups so I have used these on the site. I can't find any official codes for these so they have a "QDB" code which is entirely made up by me.


Most of the Scottish data is fairly straightforward. There seems to have been a bit of muddle about the actual identifiers for indicators and I have used those in the final publication. QS002 was used last year and then for a completely different indicator this year so I have used QS002A for the new one.


English data imported fairly easily this year, much helped by a "raw data" publication. There is a new "sub-region" which was used in publication which adds another level to the hierarchy on the site with the exception of Wessex. On the spreadsheets Wessex CCG was listed as its own sub region and to avoid a horrible loop it simply skips the sub region stage.

Northern Ireland

As things stand there is no prevalence data for Northern Ireland where there is no other indicator in that disease area. This affects obesity, epilepsy and learning disability and there is not a lot of smoking data either. I will update this if more information becomes available.

There are now Local Commissioning Groups in Northern Ireland. I have used these in much the same way as the old boards although they cover different areas, most notably by having a separate group for Belfast.

2015 Data publication dates

All of the data from this site comes from the various governments around the UK. Some of the publication dates have been announced. It takes me a little bit of time to translate this onto the site but for interest here are the dates currently available.

QOF Consultation

It is nearly the deadline for responses for the consultation by the NICE committee on potential new QOF indicators (5pm on the 23rd of February). The first that these indicators could be expected to be seen would be 2016-17 and in general the committee has been largely ignored over the last couple of years. You can read the NICE consultation papers and my response to them.