There is plenty of research out there - some of it quite technical, the following cover research from the Netherlands, UK and Australia
https://www.sciencedirect.com/science/article/pii/S2352146515001192
eprints.whiterose.ac.uk
This first one appears interesting, but having read the summary, it seems to 'prove' the opposite of what I thought it was saying! I shall have to re-read it carefully.
There are obviously a huge number of factors affecting peoples' reaction to changing trains - not least people themselves. Hence this!
Sufficiently for the ORCATS model to build in 76 passenger profiles, each with different attitudes to interchange
One thing I began to ponder was the need for a controlled comparison case. The only one I could come up with is from 50 years ago, but it might prompt someone in here to find a modern example, which in turn might even prompt some research today (depending on who reads this thread).
My case is the MML service to Derby and Nottingham back in the late 60s and 70s (and maybe even some in the 80s, but I was out of it then).
As some in here will remember, in those days there were, outside a few peak-hour extras, 2 x Class 1 TPH from St Pancras, which sought to provide an express service of 1 TPH to Leicester, Nottingham, Derby and Sheffield.
The two trains were an express - first top Leicester - and on to Sheffield, and a semi-fast to Derby or Nottingham which preceeded the express by departing St Pancras by about 30-35 mins earlier.
Thus Leicester and Sheffield got a direct 1 TPH express service, but to do the best with the resources available, the Sheffield express alternated between running via Derby one hour and Nottingham the next.
So, in the hour that the express ran via Derby, passengers for Nottingham had a very simple, cross platform connection into the semi-fast service at Leicester, where the express overtook the semi-fast and after a 4 min stop, roared off towards Trent.
Five minutes later (if all was well) the semi-fast departed for Nottingham, stopping at Loughboro'.
The next hour, the process was reversed - the express going to Sheffield via Nottingham, and the semi-fast going to Derby and stopping at Loughboro' and (at least in some years) at Long Eaton.
This was a near-perfect, practical example that could show the reluctance or otherwise of passengers to change trains.
It was also a very reliable connection, because the down express would, in 99% of cases, not be able to overtake the semi-fast, even if it was running late.
(It wasn't perfect, because there was, of course, a time-penalty of 15-20 minutes if a Derby or Nottingham passenger left the express for the semi-fast - because of the pathing delay and the one or two stops after Leicester.)
I have no idea if any research was done at the time, and sadly, I never thought to try to assess the passenger numbers changing in any serious manner when at Leicester in those days. But, my impression, for what it's worth 50 years later, is that not that many people took advantage of this most convenient change - perhaps 20 - 30 passengers in most cases during the day, and this would include Loughboro' and Long Eaton passengers. (I wasn't often at Leicester in the evening peak, ie around 17.30 - 19.00, when numbers would probably have been more.)
In other words, I'd guess something like 75% of Derby and Nottingham passengers opted for the direct express every two hours, rather than bother with the change and slightly poorer schedules on the semi-fast. (I must stress I am only estimating these numbers from impressions at the time, and I could be just plain wrong.)
Interestingly, going in the up in those days would also be a fascinating study, because - as opposed to catching the Sheffield express service - any passengers from Derby or Notthingham opting for the semi-fast and changing would also face the problem of finding a seat on the express at Leicester.
In comparison, finding a seat on the express at Derby or Nottingham would be easier, and even in a crowded train, they would get first chance at Leicester as passengers left the train.
This long-gone example begs the question: are there any similar services on the network today where the 'change reluctance' factor could be measured in practice? Possibly on the Southern networks somewhere?