I fail to understand how you can reasonably model an unprecedented event in modern history. We have no data on how people will act under a weeks, even months long lockdown. Will they stay indoors and follow guidelines? Maybe. Will they watch their livelihoods get affected, their mental health deteriorate, or get careless over time and break quarantine? Maybe.
We just don't know because we just don't have the data or heck, even anecdotal evidence from similar events in the past
If you look at the models, they have something like an order of magnitude uncertainty. And the reason for that is precisely what you are stating, they rely on future behavior, which we just don't know yet.
However, the utility of the models is to give us a sense of how the different parameters interact. There are parts of the model were we can have a lot of trust, for example that people with severe conditions will need hospitalization, or that people will react quite similar as they reacted yesterday. So for the short term, the models give us quite good guidance, and for the long term, they help to map out scenarios.
So if you actually look at the report in question, you will see that they are actually trying to estimate the impact of various non medical interventions, like encouraging social distancing, by comparing different countries. It is just that newspapers as usual just run with the most immediately digestible number, independent wether that number is important or useful.
On the contrary, epidemics are reasonably easy to model (at least at a basic level), and modelling them has a long academic tradition. As with all modelling, it all depends on what kind of detail you want to get out of your analysis/predictions.
If you‘re looking at a simple population infection model, lockdown efficacy is just a factor affecting the contact rate among uninfected actors. You run multiple scenarios for multiple levels of this factor, and see where that gets you.
Or did you mean something else?
(Source: I‘m not an epidemiologist, but as an ecological modeller I work with very similar tools.)
So many of the models I've seen focus on the efficacy of lockdowns in controlling the spread of the disease. Most treat the length of the lockdown as a mathematical variable - X week lockdown leads to Y infection rate.
My point is that we can't reasonably predict how people will behave in lockdown past a certain point. We've never had similar lockdowns in a world that was as globalized, as hyper connected as ours. You could go from 2 to 8 weeks of lockdowns if everyone was living in isolated villages a la 1918 Spanish Flu, but that's not our present world.
How do you model a situation where after 4 weeks of lockdowns, a social media post about food shortages goes viral, causing mass panic and breaking of quarantine?
We can't because we've never had a situation like this, or the tools for spreading (mis) information as we currently do.
More importantly, the mortality, while much higher than flu, it's still relatively low.
Now imagine a virus as contagious as this one, but with 10% mortality over all age groups. That would be unprecedented and probably cause society meltdown.
How do you reckon social media will impact your models? Rumors and information - real or fake - has never been easier to spread in the world (Wuhan's data becomes less relevant here). We've already seen calls for defiance of lockdowns in right wing circles. In my country, old videos are being circulated to spread misinformation about the treatment.
Again, our data for all older epidemics is applicable to the epidemic in isolation. But there is no way to accurately model how the epidemic interacts with people simply because the way people live has changed drastically from past epidemics.
We just don't know because we just don't have the data or heck, even anecdotal evidence from similar events in the past