# Calculate National Trends in International Large-Scale Assessments

### Description

This function processes LSA data and returns trend estimates in latent variable means and proficiency level frequencies.

### Usage

1 2 3 4 5 6 | ```
eatTrend(itParsIntT1, PVsT1, countriesT1, itParsNatT1=NULL,
jkzoneT1=NULL, jkrepT1=NULL, weightsT1=NULL, groupsT1=NULL, itParsIntT2, PVsT2,
countriesT2, itParsNatT2=NULL, weightsT2=NULL, jkzoneT2=NULL, jkrepT2=NULL,
groupsT2=NULL, GES=TRUE, testletNam = NULL, transfTo500=TRUE, mtT=500, sdtT=100,
mRefPop=NULL, sdRefPop=NULL, cutScores=NULL, type =c("FCIP", "MM"), writeCsv=FALSE,
path=NULL, plots=FALSE, backwards=FALSE, groupNam=NULL, landNam=TRUE, FRZ=FALSE)
``` |

### Arguments

`itParsIntT1` |
A data frame containing the international item parameter estimates at time 1. The first column has to be an ID variable, the second column contains the estimates. |

`PVsT1` |
A data frame containing plausible values for all persons at time 1. The first column has to be an ID variable, the following columns contain plausible values. |

`countriesT1` |
A vector containing the group membership for every person at time 1. The order
has to correspond to the ID column in |

`itParsNatT1` |
A list of data frames. The lists' names should correspond to the groups specified
in |

`jkzoneT1` |
A vector containing the primary sampling unit at time 1. The order
has to correspond to the ID column in |

`jkrepT1` |
A vector containing the jackknife replicate ID at time 1. The order
has to correspond to the ID column in |

`weightsT1` |
A vector containing the case weights at time 1. The order
has to correspond to the ID column in |

`groupsT1` |
A vector or a data.frame indicating subgroup-membership ("1") or subgroup- nonmembership ("0") at time 1. |

`itParsIntT2` |
A data frame containing the international item parameter estimates at time 2. The first column has to be an ID variable, the second column contains the estimates. Please assure that the item parameters stem from an analysis in which the person parameters were centered around zero or that an equivalent adjustment has taken place. |

`PVsT2` |
A data frame containing plausible values for all persons at time 2. The first column has to be an ID variable, the following columns contain plausible values. Please note that the columns should be centered around zero. |

`countriesT2` |
A vector containing the group membership for every person at time 2. The order
has to correspond to the ID column in |

`itParsNatT2` |
A list of data frames. The lists' names should correspond to the groups specified
in |

`jkzoneT2` |
A vector containing the primary sampling unit at time 2. The order
has to correspond to the ID column in |

`jkrepT2` |
A vector containing the jackknife replicate ID at time 2. The order
has to correspond to the ID column in |

`weightsT2` |
A vector containing the case weights at time 2. The order
has to correspond to the ID column in |

`groupsT2` |
A vector or a data.frame indicating subgroup-membership ("1") or subgroup- nonmembership ("0") at time 2. |

`GES` |
Logical. If |

`testletNam` |
Character vector containing the names of the units/testlets in which items are clustered. |

`mtT` |
Numeric. Mean of arbitrary metric to which parameters are transformed. |

`sdtT` |
Numeric. Standard deviation of arbitrary metric to which parameters are transformed. |

`mRefPop` |
Numeric. The mean of the reference population. |

`sdRefPop` |
Numeric. The standard deviation in the reference population. |

`transfTo500` |
Logical. If |

`cutScores` |
Named vector indicating the proficiency level cut scores in descending(!) order.
If is not |

`type` |
Character. If |

`writeCsv` |
Logical. If |

`path` |
A character string containing the path for the output files. |

`plots` |
Logical. If |

`backwards` |
Logical. IQB internal option to transform cutScores internally. |

`groupNam` |
A character vector containing group names. |

`landNam` |
Logical. Bundesland-Klarnamen. |

`FRZ` |
Logical. Standardisiert PV-weise wenn FALSE. |

### Value

A list with two data frames: Countrywise trends in means and proficiency levels.

### Author(s)

Karoline Sachse