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

*
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 - (sigma2/sigma1)^2)*

where
*sigma1* is the fixed effects RSD and *sigma2*
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))))

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