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This plugin estimates parameters under Item Response Theory approach, using the <link href="rkward://rhelp/ltm-package">ltm</link> package.
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To fit the Rasch model with default settings, just the matrix of manifest variables (dichotomous item responses) must be selected. Further options are described in the sections below.
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The complete results are stored as a new object in the current workspace for further use (e.g. plotting item characteristic curves). This object will be called <code>estimates.rasch</code>.
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<caption id="tab_data"/>
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<setting id="x" title="Matrix of manifest variables">
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Select the matrix of dichotomous item responses from the objects shown on the left.
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<caption id="tab_options"/>
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<setting id="frame_constraints">
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If you want to fix parameters, you have to prepare a matrix of fixed-value constraints first and then select it here. For detailed information on the specific layout of that matrix please refer to the manual for the <link href="rkward://rhelp/rasch">rasch()</link> function.
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<setting id="startval">
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By default start values for the parameters are computed automatically. Alternatively, you can force the use of random start values, or give a matrix of values to be used. For detailed information on the specific layout of that matrix please refer to the manual for the <link href="rkward://rhelp/rasch">rasch()</link> function.
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<setting id="naaction">
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Specifies how missing values are to be treated. By default all available cases are used. If checked, only complete cases will be considered.
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<setting id="irtparam">
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If checked, the coefficients' estimates are reported under the usual Item Response Theory parameterization (which is the default).
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<caption id="tab_advanced_control"/>
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<setting id="iterqn_rasch" title="Number of quasi-Newton iterations">
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<setting id="ghk_rasch" title="Number of Gauss-Hermite quadrature points">
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<setting id="optimeth" title="Optimization method">
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The default optimization method is BFGS. It can be set to Nelder-Mead, CG, L-BFGS-B, or SANN instead. Please refer to the <link href="rkward://rhelp/optim">optim()</link> manual for details.
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<setting id="verbose">
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Pretty much speaks for itself ;-)
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Please refer to the <code>ltm</code> manuals for further information and detailed command line options:
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<li><link href="rkward://rhelp/ltm-package"/></li>
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<li><link href="rkward://rhelp/rasch"/></li>
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