Default priors in brms #10
Description
The default priors for population effects are currently normal(0,100). This seem a little too diffuse for a default so should probably be tightened. Also the model will always try to set priors for population level effects, which leads to a an error if fitting models with no population effects. Finally, the model currently uses a flat improper prior for the intercept. Would be good to change this a potentially. Also should probably add the specification of this to an example somewhere as this is essentially setting the prior on the inverse link of the population prevalence (not quite because the population and group effects mess things up a little). Since people might generally have a pretty good idea of what they expect prevalence to be, this might be a parameter with a fair about prior knowledge to work with. However it's also one of the more identifiable parameters, so prior knowledge mightn't be that necessary