plotDIF {eRm} | R Documentation |

Performs an plot of item parameter conficence intervals based on `LRtest`

subgroup splitting.

```
plotDIF(object, item.subset = NULL, gamma = 0.95, main = NULL,
xlim = NULL, xlab = " ", ylab=" ", col = NULL,
distance, splitnames=NULL, leg = FALSE, legpos="bottomleft", ...)
```

`object` |
An object of class |

`item.subset` |
Subset of items to be plotted. Either a numeric vector indicating the items or a character vector indicating the itemnames. If nothing is defined (default), all items are plotted. |

`gamma` |
The level for the item parameter's confidence limits (default is gamma = 0.95). |

`main` |
Main title for the plot. |

`xlim` |
Numeric vector of length 2, giving the x coordinates ranges of the plot (the y coordinates depend on the number of depicted items). |

`xlab` |
Label for the x axis. |

`ylab` |
Label for the y axis. |

`col` |
By default the color for the drawn confidence lines is determined automatically whereas every group (split criterion) is depicted in the same color. |

`distance` |
Distance between each item's confidence lines – if omitted, the distance shrinks with increasing numbers of split criteria. Can be overriden using values in (0, 0.5). |

`splitnames` |
For labeling the splitobjects in the legend (returns a nicer output). |

`leg` |
If |

`legpos` |
Position of the legend with possible values |

`...` |
Further options to be passed to |

If there are items that cannot be estimated for some reasons, certainly these ones are not plotted.
For plotting several objects of class `LR`

, the subgroup splitting by `LRtest`

has to
be carried out for the same data set (or at least item subsets of it).

Plotting a certain subset of items could be useful if the objects of class `LR`

contain a huge number
of estimated items.

The default level for the conficence limits is gamma = 0.95. (If the conficence limits should be corrected it is useful to use a correction, e.g., Bonferroni: 1 - (1 - gamma) / number of estimated items.)

`plotCI`

returns a list containing the confidence limits of each group in each `LRtest`

object.

Kathrin Gruber, Reinhold Hatzinger

`LRtest`

, `confint.threshold`

, `thresholds`

```
# the object used is the result of running RM(raschdat1)
res <- raschdat1_RM_fitted # see ? raschdat1_RM_fitted
## Not run:
# LR-test on dichotomous Rasch model with user-defined split
splitvec <- rep(1:2, each = 50)
lrres <- LRtest(res, splitcr = splitvec)
# LR-test with mean split
lrres2 <- LRtest(res, split = "mean")
# combination of LRtest-objects in a list
RMplotCI <- list(lrres, lrres2)
## End(Not run)
# the object raschdat1_RM_plotDIF is the result of the computations outlined
# above and is loaded to save computation time. see ?raschdat1_RM_plotDIF
RMplotCI <- raschdat1_RM_plotDIF
# Confidence intervals plot with default assumptions
plotDIF(RMplotCI)
# Confidence intervals plot with Bonferroni correction
plotDIF(RMplotCI, gamma = (1 - (0.05/10)))
# Confidence intervals plot for an item subset
plotDIF(RMplotCI, item.subset = 1:6)
# with user defined group color and legend
plotDIF(RMplotCI, col = c("red", "blue"), leg = TRUE, legpos = "bottomright")
# with names for the splitobjects
plotDIF(RMplotCI, col = c("red", "blue"), leg = TRUE, legpos = "bottomright",
splitnames = c(paste("User", 1:2), paste(rep("Mean", 2), 1:2)))
```

[Package *eRm* version 1.0-2 Index]