We've been looking closely at the NHS Template for SPC charts and came across a few problems with it.
The latest "Statistical process control tool" template can be downloaded from
We downloaded our copy on 25th August 2021. The file was created on 02/05/2017 11:02 but the filename is SPC-tool-excel-201-20200915, which may suggest a date of 15th September 2020 for this release.
Here's a screen shot of the chart we generated with the Template here.
Note the the "variation icon", the leftmost of the two icons. That's shown as an orange "F".
The rules for this icon are:
If last 6 performance points are:
- better than target = show P icon
- worse than target = show F icon
- a mix of better and worse = show ? icon
Defect 1: Inconsistent compute and display of icons
The rules are arguably ambiguous as to what happens should a point be precisely "on target", but the template chart code colours this point blue, which is correct as it's actually a little better than the target.
However the variation icon, which depends directly on this point and the subsequent five compared against the target is coloured orange.
They can't both be right, so at least one of them is wrong.
Defect 2: The "variation icon" is incorrect
It's coloured orange and marked F - it should be a blue L.
As above, all the last 6 points exceed the target requirement, so the chart happens to be correct in this case, and the "variation icon" drawn on it must be wrong.
For this example the sixth from last point (point 16 in the full resolution data table shown here) is 01-03-2021 and has a database value of precisely 0.91445881182747. If one was to round that to two decimal places you'd get 0.92, which would appear to be "on target", but the spreadsheet claims the target is not met. Our guess is that the spreadsheet may be incorrectly rounding the data, and also incorrectly and inconsistently testing compliance against the target.
Recorded as Public View Issue #1604: NHS Template SPC-tool-excel-201-20200915 multiple errors
This isn't an exhaustive list of issues.
- Updated Stroke Metrics 15 Oct 2021
- User Interface Updates 11 Oct 2021
- 287 Metrics 07 Oct 2021
- Automated Testing 20 Sep 2021
- New Release 09 Sep 2021
- New User Defined Reports 04 Sep 2021
- NHS Template Errors 26 Aug 2021
- Templates Direct Database Connexion 26 Aug 2021
- Statistical Process Control (XmR) Tool 25 Aug 2021
- Public View Database Service 23 Aug 2021
- User Defined Pages Beta 22 Aug 2021
- New Top Level SPC Icons 18 Aug 2021
- Public View World Wide 14 Aug 2021
- Public View G Cloud 13 Aug 2021
- Public View Database Service 06 Aug 2021
- More SPC Chart Goodness 05 Aug 2021
- A New Blog Site 04 Aug 2021
- Release 1.4, Database Access 29 Jul 2021
- New SPC Charts 02 Jul 2021
- New Maternity Indicators 02 Jul 2021