BICadj | R Documentation |

`BICadj`

and `AICadj`

calculate the BIC and AIC for SITAR models,
adjusting the likelihood for Box-Cox transformed y variables. `varexp`

calculates the variance explained by SITAR models, compared to the
corresponding fixed effect models. `getL`

is used by `[AB]ICadj`

to
find what power the y variable is raised to.

```
BICadj(..., pattern = NULL)
AICadj(..., k = 2, pattern = NULL)
varexp(..., pattern = NULL)
getL(expr)
```

`...` |
one or more SITAR models. |

`pattern` |
regular expression defining names of models. |

`k` |
numeric, the penalty per parameter to be used; the default k = 2 is the classical AIC. |

`expr` |
quoted or unquoted expression containing a single variable name. |

The deviance is adjusted if the y variable is power-transformed, using the formula

```
adjusted deviance = deviance - 2n ( (\lambda-1) * log(gm) + %
log(abs(\lambda)) )
```

where `\lambda`

is the power transform, and `n`

and
`gm`

are the length and geometric mean of `y`

.

The variance explained is given by

```
\% explained = 100 * (1 -%
(\sigma_2/\sigma_1)^2)
```

where
`\sigma_1`

is the fixed effects RSD and `\sigma_2`

the SITAR random effects RSD.

`BICadj`

and `AICadj`

accept non-`sitar`

models with a
`logLik`

class. `varexp`

ignores objects not of class
`sitar`

.

`getL`

does not detect if the variable in `expr`

, or its log, contains a multiplying constant,
so that the expressions `log(x)`

and `1 + 2 * log(3 * x)`

both return 0.

For `BICadj`

and `AICadj`

a named vector of deviances in
increasing order. For `varexp`

a named vector of percentages in
decreasing order. For `getL`

the power the variable in `expr`

is raised to, or `NA`

if `expr`

is not a power of (a multiple of)
the variable.

Tim Cole tim.cole@ucl.ac.uk

`BIC`

, `AIC`

```
data(heights)
## fit sitar model for height
m1 <- sitar(x=age, y=height, id=id, data=heights, df=5)
## update it for log(height)
m2 <- update(m1, y=sqrt(height))
## compare variance explained in the two models
varexp(m1, m2)
## compare BIC adjusting for sqrt transform
## the pattern matches names starting with "m" followed by a digit
BICadj(pattern="^m[0-9]")
## find what power height is raised to
getL(quote(sqrt(sqrt(height))))
```

Embedding an R snippet on your website

Add the following code to your website.

For more information on customizing the embed code, read Embedding Snippets.