Comparing Locrating catchment indicators with local authority cut off distances
We're quite regularly asked why our catchment indicators do not match exactly the data shown on local authority websites. The short answer is because they are showing slightly different things. The long answer is below.
The problem with local authority data
One of the problems we came across early on, when building the site, was that whilst some local authorities publish cut-off distances, others don’t and the ones that do don’t always publish for all schools. Plus, the information is presented in a myriad ways, with each local authority having their own maps, pdfs and web pages; all presenting the data in slightly different ways.
We quickly realised that we weren't going to be able to work with this data for the 30k+ schools that we hold data on; it would require simply too much manual analysis and data entry. So, we investigated alternative sources of information.
Update February 10, 2020: Since writing this blog post, we have now started collecting data from council websites, see Collecting last distance offered data.
The National Pupil Database
After some failed attempts with Freedom on Information requests, we ended up turning to the National Pupil Database (NPD), which is essentially a database of all children in England; including where they live and what school they go to.
Because we could see where existing pupils lived and break that down by year group, we were able to plot where the latest intake of children live on our map.
The application process for access to this data is rightly long and arduous, as it is highly sensitive information about our children, but we made our case for the public benefit and following approval by an ethics committee were granted access. This information, incidentally, is totally free for all!
It provided consistent data for all schools across England, which we could work with. Because we can see where existing pupils live, we are able to plot where the latest intake of children live on our interactive map. There is more detail on exactly how we do this in our blog article Locrating's catchment areas explained.
A crystal ball
The theory is that by showing where the most recent intake of pupils live, with the ability to look back in time over a number of years, we can provide a reasonable indication as to where future pupils will likely live. Which is useful for people considering moving to an area or when looking for schools their children in their local area. However, this comes with a few very important caveats.
The past is not a predictor of the future!
The biggest of all is that the past is not a predictor of the future. As a perfect example, we have friends who have neighbours on either side of them whose children attend our friends' preferred school. These children got in before and after our friends applied for their child and yet our friend's child was not offered a place, why? Because it just so happened that in the year our friend's child applied, more children lived closer to the school than in the years before and after; just bad luck.
So many factors are in play that it's impossible to guarantee entry based on an address, so all distances, from us (or anywhere else) need to be treated with caution. We have an interesting article on these issues in our blog post catchment area myths.
What does local authority data show
Going back to the local authority data, some, but not all schools will offer a place to siblings over distance (amongst a range of different admissions criteria that schools may have, even including lotteries!) and this is where the local authority data can be very helpful, because when they publish a distance based on the 'distance criterion' it has siblings excluded; in fact not just siblings, they exclude children in care, with SEN and all those that were offered a place not based on their distance from the school.
A 'distance criterion' cut-off distance from a local authority, is the distance of the last child who was offered a place based solely on their distance from the school.
This means that a 'distance criterion' cut-off distance from a local authority, is the distance of the last child who was offered a place based solely on their distance from the school.
What does Locrating data show
We show where all children, including siblings live, broken down by area and year group. It would be nice to be able to exclude siblings (where appropriate - remember not all schools have a sibling policy), but unfortunately the NPD database does not have a sibling indicator (nor details of school admission policies).
Although we do exclude children in care and with SEN as those markers do exist in the NPD and those children are almost always offered a place above other children; so can be justifiably excluded.
So, both pieces of data are totally correct and from official sources of information, but they show slightly different things. This is where any differences between the local authority data and our data come from; it's typically caused by siblings in schools that have both a sibling priority and a distance criterion. These siblings can live further from the school and make the catchment appear bigger on Locrating than it actually was for non-siblings.
So, does this mean the local authority data is more useful than Locrating's; not at all, because they show different and equally important pieces of information. Where possible you want to look at both!
The benefits of it all
So, does this mean one piece of data is more useful than the other; not at all, because they show different and equally important pieces of information.
We shade postcode type areas at a street level, indicating where the latest intake of pupils live, you can't get this from a simple distance and where this becomes important is if the school has a priority area, e.g. it's on a local authority boundary. You can use Locrating to look back over time and you'll spot areas that are close, but never have children accepted from; that indicates that something else other than distance is at play.
We also show a heatmap of pupil concentration, which you can't get from a single number, this shows where the majority of children live and gives further valuable insight into your chances of being offered a place at the school.
For example, you might find 80% of the children are within 1000m (the green and yellow areas on our map) and only 10% within 2000m (the red area on our map). If the intake is only 30 children, then the bulk of that extra 1000m may be caused by just one child! So you should focus more on the 1000m number, instead of the 2000m.
We strongly advise you speak to schools directly (they’re usually very friendly and helpful); as there may be a bulge year (meaning extra students are taken that year) or some other factor in play that means next year’s intake is expected to be very different from previous years. They can also explain their admissions policy to you in detail.
We also recommend you look at the local authority website to see if they have published any cut-off distances that excludes siblings, for schools that have a sibling policy. They may also publish how many siblings were offered a place, which you can use to add context to our maps, e.g. if 15 of 30 were siblings, you need to be looking more at the green areas that show where the majority of pupils live rather than the red areas. But if only 1 was a sibling then you can focus more on the entire shaded area.
Remember, the red represents a very small percentage of pupils, so it makes sense to almost ignore that and focus on the green and closer parts of the yellow areas; where the bulk of the pupils live.
We further recommend you use our site as follows:
- Look at the shaded blue areas for the last year and also previous years (via the menu you can change the academic year to go back 4 years); what you are looking for here are areas that never highlight. That would indicate there is some reason for this; such as the school is on a local authority boundary or has a preferential area elsewhere (children from this area get preference over others). Ideally you would see the area you are interested in being highlighted at least once to show that someone has been accepted from there in the past few years.
- Look at the shaded circles; the further out of the shading your location is the less children that live there. The 'catchment over time' popup on the bottom left shows how this circle changes over time. Big swings in the yellow/red are showing how the last children to be offered might vary by quite some distance from one year from the next. So, if you are in one of these areas that only sometimes appears shaded in yellow or red, the your chances may be likely to big swings from one year to the next.
- Remember, the red represents a very small percentage of pupils, sometimes just one child, so it makes sense to almost ignore that and focus on the green and closer parts of the yellow areas; where the bulk of the pupils live.
- In general, if you’re in a green area of the shaded circle, that’s also in a drawn blue area your chances are good. If in a yellow or red area - your chances are less good, if your area of interest never appears in blue for any of the past 5 years, then you definitely need to call the school to see why.
- You can change the year group for the blue shaded areas; for primary schools, it might be worth looking at Year 1 as well as reception, as some schools can admit directly into Year 1 (again something to check with the school on).
The local authority data will be available before our data; as we need to wait for children to start at the school and to make their way onto the NPD, whereas local authorities can publish information much sooner, after the offers have gone out.
I don't know if local authority data factors in offers that were not accepted, this is important as it will change the meaning of the numbers, e.g. if the last offer was to someone 500m away, but they turned that offer down (for a different school) then the place could go to someone 750m away instead, does the local authority record 500m or 750m; it's not clear to me, i.e. is the data from first round offers only?NPD data is based purely on children who accepted their offers and joined the schools.
I hope that helps and good luck with your search!
Author: Lewis Tandy