This function is a constructor for the `cor_arma`

class,
allowing for moving average terms only.

`cor_ma(formula = ~1, q = 1, cov = FALSE)`

formula

A one sided formula of the form `~ t`

, or `~ t | g`

,
specifying a time covariate `t`

and, optionally, a grouping factor `g`

.
A covariate for this correlation structure must be integer valued.
When a grouping factor is present in `formula`

, the correlation structure
is assumed to apply only to observations within the same grouping level;
observations with different grouping levels are assumed to be uncorrelated.
Defaults to `~ 1`

, which corresponds to using the order of the observations
in the data as a covariate, and no groups.

q

A non-negative integer specifying the moving average (MA) order of the ARMA structure. Default is 0.

cov

A flag indicating whether ARMA effects should be estimated
by means of residual covariance matrices
(currently only possible for stationary ARMA effects of order 1).
If `FALSE`

(the default) a regression formulation
is used that is considerably faster and allows for ARMA effects
of order higher than 1 but cannot handle user defined standard errors.

An object of class `cor_arma`

containing solely moving average terms.

```
# NOT RUN {
cor_ma(~visit|patient, q = 2)
# }
```

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