Two weeks ago I wrote about different methods to obtain party positions on immigration. I compared different methods, including manifesto-based ones. You can check out the figures, including two not included in the research note.
With the short extracts on immigration, I was unable to get realistic party positions on immigration using Wordfish. Interestingly, using just a few additional documents (the way CMP controversially does it) seems to lead to realistic estimates.
Part of the research note is about a retrospective survey to place parties. I basically asked my colleagues how the parties are placed today and in the past 20 years. None of them works on parties. Taking the average does yield surprisingly good estimates, as outlined in the research note. Unsurprisingly, the standard deviations are large, but they are not uniform or simply larger the further back we go.