| ExchFixed {demest} | R Documentation |
A simpler exchangeable prior than Exch. The units are
assumed to be drawn from a normal distribution with no covariates and
a known standard deviation.
ExchFixed(mean = 0, sd = NULL, mult = 1)
mean |
Mean. Optional. |
sd |
Standard deviation. Optional. |
mult |
Multiplier applied to |
The prior specified by ExchFixed has the form
parameter[j] ~ N(mean, sd^2).
mean defaults to 0. In most cases, non-zero means are ignored,
with a warning, when the model is generated. The exception is when
ExchFixed is being used to specify an intercept term,
when generating simulated data.
If a value for sd is not supplied by the user, then a value is
generated when function estimateModel,
estimateCounts, or estimateAccount is called.
Let s be the standard deviation of data y, or of log(y)
in the case of a Poisson model without exposure, and let m be
the mult argument. The default value for sd is then
| Model | Default |
| Poisson with exposure | m |
| Poisson without exposure | ms |
| binomial | m |
| normal | ms. |
These value are designed to be weakly informative, in that they favour
values for sd that are demographically plausible.
ExchFixed can be useful a dimension with few elements, such as sex
dimension, where there is insufficient information to justify more
complicated priors.
An object of class SpecExchFixed.
Exch specifies a more complicated
exchangeable prior.
## default standard deviation ExchFixed() ## user-specified standard deviation ExchFixed(sd = 0.5) ## reduce the size of the automatically-generated 'sd' ExchFixed(mult = 0.5) ## increase the size of the automatically-generated 'sd' ExchFixed(mult = 2)