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The Stata module "Raschfit"
Raschfit realizes the Raschfit algorithm defined by Hardouin and Mesbah (2004). This method selects sub-scales of items which fit a Rasch model. The method begin with a kernel of items (two or more items) defined by the user. At each step, the method uses a new item and verifies if this new item is explained by the same latent trait than the already selected items. If not, the items is not selected. The former version of the Raschfit algorithm is based on the comparison of two model: A Rasch model and a Multidimensional Marginally Sufficient Rasch Model (MMSRM). These two models are compared by the Akaike Information Criterion (AIC). A faster version of the algorithm (Raschfit-Fast) compares the Rasch model and an adapted version of this model where the response to the "new" item is not explained by the latent trait. Raschfit-Fast is executed by default.
Type "findit raschfit" or "ssc install raschfit" directly from your Stata browser.
Syntax (version 4)
raschfit varlist [, kernel(#) nbscales(#) itemsorder(order/msp/mspinv) nofast ]
This program requires an access to the following program(s):
Only the individuals with none missing values are used.
- kernel(#): defines the # first items of varlist as the kernel of the first sub-scale (by default, this number is fixed to 2).
- nbscales(#): defines the maximal number of sub-scales (by default, only one sub-scale is selected)
- itemsorder(order/msp/mspinv): defines the order of the items. If you type order, the kernel is composed of the first items defined in varlist, and the items are tested in the same order than in varlist. If you type msp or mspinv, a Mokken Scale Procedure is run under the items and the items are selected from the first order selected by this procedure to the last one (with msp), or in the inverse order (with mspinv). The method msp is generaly more robust, but is longer to run. By default, the program uses msp.
- nofast: runs the Raschfit procedure instead of the Raschfit-fast procedure
raschfit itemA* , itemsorder(order)
raschfit itemA1-itemA7 , itemsorder(msp) kernel(4) nofast