Parameterise onset type better #45
Description
Follow on from #34
I've made a rough guesstimate based on https://strokeaudit.org/SupportFiles/Documents/Posters-and-oral-presentations/2020/ESOC-2020-Onset-to-arrival-times_Poster.aspx but this lacks a split by day and night.
There's also the complexity of estimating what percentage of unknown onset might be within a thrombolysable window with CTP in the mix, which is even harder to ascertain. I've had a look at various papers but no completely satisfying estimates to work with.