As a workaround, could one use the brms weight argument to add one made-up datapoint (i.e., population mean) per new location, and then apply zero weights to said datapoints? This could be very wrong, but it feels so right.
As a workaround, could one use the brms weight argument to add one made-up datapoint (i.e., population mean) per new location, and then apply zero weights to said datapoints? This could be very wrong, but it feels so right.