﻿ Graph window

# Graph window

If you don't see all this on your screen, you may have your screen resolution set to 800 x 600 pixels. Try setting it to 1024 x 768. Windows "Start", "Settings", "Control Panel", "Display", "Settings", Move "Screen resolution" slider to the right.

Category Probability Curves: (Probability Cat. Curves) model-based probability of observing each category of the response structure at each point on the latent variable (relative to the item difficulty)

Empirical Category Curves: (Empirical Cat. Curves) data-based relative frequencies of categories in each interval along the latent variable

Category Model and Empirical Curves: (Prob.+Empirical Cat. Curves) the model-based and data-based frequencies of each category.

Expected Score ICC shows the model-based Item Characteristic Curve (or Item Response Function IRF) for the response structure.

Empirical ICC shows the data-based empirical curve.

Cumulative Probabilities plot the model-based sum of category probabilities. The category median boundaries are the points at which the probability is .5. Click on a line to obtain the category accumulation.

Conditional Probability Curves show the model-based relationship between probabilities of adjacent categories. These follow dichotomous logistic ogives. Click on a line to obtain the category pairing.

Item Information Function plots the model-based Fisher statistical information for the item. This is also the model variance of the responses, see RSA p. 100.

Category Information plots the model-based item information partitioned according to the probability of observing the category. Click on a line to obtain the category number.

Test Information Function - this can be plotted with Excel.

 Button or Slider Function Adjust maximum Y-value Sets the maximum value on the vertical Y-axis Adjust Y-axis divisions Sets the number of tick-marks on the Y-axis Copy Plot to Clipboard Copies the graph to the Windows clipboard. This only copies the part of the plot that is visible on your screen. Maximize the chart window and increase your screen resolution if the entire plot is not visible. To increase screen resolution: Windows "Start", "Settings", "Control Panel", "Display", "Settings" and move the "Screen resolution" slider to the right. Open a graphics program, such as Paint, and paste in the image for editing. Copy Data to Clipboard Copies the graphed numbers to the Windows clipboard (for pasting into Excel, etc.) Use paste special to paste as a picture meta-file, bitmap or as a text listing of the data points. Each row corresponds to a set of points to plot: Column A - ignore (internal row identifier) Column B - x-axis for point on first curve: measure relative to item difficulty or relative to latent variable Column C - y-axis for point on first curve: probability, expected score, etc. Column D - x-axis for point on second curve: measure relative to item difficulty or relative to latent variable Column E - y-axis for point on second curve: probability, expected score, etc. etc. Scatterplot: Column C (y-axis) against Column B (x-axis) Column E (y-axis) against Column D (x-axis) etc. Combined plots: the curves on two or more Facets graphs can be combined into one Excel plot using "Copy Data" from the different graphs into one Excel worksheet. Next Curve Displays the same graph for the item with the next higher entry number. Select Curves Displays the graph for the selected item from the curve-selection-box: Previous Curve Displays the same graph for the item with the next lower entry number. Probability Cat. Curves Displays the Rasch-model probability-curve for each response-category Prob+Empirical Cat. Curves Displays the Rasch-model probability-curve for each response-category, together with the empirical curve summarizing the data in each empirical interval. Empirical Cat. Curves Displays the empirical curve for each response-category, summarizing the data in each empirical interval Prob+Empircal Option Curves Displays the Rasch-model probability-curve for each response-option, together with the empirical curve summarizing the data in each empirical interval. Empirical Option-Curves Displays the empirical curve for each response-option, summarizing the data in each empirical interval Expected Score ICC Displays the expected-score item characteristic curve, the item's Rasch-model logistic ogive. Exp+Empirical ICC Displays the expected-score item characteristic curve, the item's Rasch-model logistic ogive, together with the empirical ICC summarizing the data in each empirical interval. Empirical ICC Displays the item's empirical item characteristic curve, summarizing the data in each empirical interval. Cumulative Probabilities Displays the Rasch-model cumulative probability-curve for each response-category and the categories below it. Conditional Probabilities Displays the Rasch-model probability-curve for the relative probability of each adjacent pair of categories. These are dichotomous ogives. Item Information Displays the item-information function according to the Rasch model. Category Information Displays the information function for each category according to the Rasch model. Test Information Displays the test-information function according to the Rasch model. The inverse square-root of the test information is the standard error of the Rasch person measure. Click on line for description Click on a curve to show its description below the graph. You can identify an individual traceline by single-left-clicking on it. Its description will then appear below the plot. Click elsewhere on the plot to remove the selection indicators. Double-click to erase line You can remove a traceline by double-left-clicking on it. Click on the command button, e.g., "Probability Curves", to return the plot to its initial appearance. Display Legend Hide Legend Click on "Display legend" to show descriptions of all the curves below the graph. Click on "Hide legend" to remove the descriptions. Absolute x-axis Relative x-axis Click on "Absolute x-axis" to show the graphs with measures on the latent variable along the x-axis. Click on "Relative x-axis" to show the graphs with the x-axis plotted relative to the item difficulty. Points, Lines, None, Both Click on this button to show the empirical curves as both points("x") and lines, points only, lines only, and neither points nor lines. Adjust minimum Y-value Sets the minimum value on the vertical Y-axis Smoothing Controls the degrees of smoothing of the empirical curve Set Color Click on a curve to select it, the click on "Set Color" to change its color using the color-selection-box. Help Click on Help to display this page. Adjust minimum X-value Sets the minimum value on the horizontal X-axis Fine-tune minimum X-value Makes small changes to the minimum value on the horizontal X-axis Adjust X-axis divisions Sets the number of tick-marks on the X-axis Empirical divisions (slider) Sets the number of empirical summary-intervals on the X-axis Empirical divisions (arrows) Makes small changes to the number of empirical summary-intervals on the X-axis Fine-tune maximum X-value Makes small changes to the maximum value on the horizontal X-axis Adjust maximum X-value Sets the maximum value on the horizontal X-axis

Curve selection Box

 This box displays the item entry numbers and labels. Click on the item which you want displayed.

ICC Selection Box

 To select the curves: click on the cells and they will turn green to indicate which curves are selected for display. Then click OK to display the curves.

Color Selection Box

 Click on desired color, and then OK

The probability curves will display. Graphs are plotted relative to the central difficulty of each item or scale group.

The buttons are:

Copy Plot to Clipboard places this plot on the clipboard as a graphic. Open a graphics program, such as Paint, and paste in the image for editing, or paste directly into a Word document.

Copy Plot Data to Clipboard places the plotted data on the clipboard. This can be pasted into an Excel worksheet so that you can use it to construct your own graphs.

Next Curve takes you to the curves for the next Group.

Previous Curve takes you to the curves for the previous Group.

Select Curves enables you to jump to the set of curves you want to see by clicking on the list that is displayed. Click on the desired curve.

Probability Cat. Curves plots the category probability curves according to the model. There is one curve for each category. They sum vertically to 1.0. Click on a line to obtain the category.

Empirical Cat. Curves plot the empirical category frequency points according to the data. The points are joined by lines for ease of viewing.

Prob.+Empirical Cat. Curves plots both the model and empirical category curves.

Expected Score ICC plots the model-expected item characteristic curve, and the empirical one, shown by X. One curve is shown for each rating (or partial credit) scale.

Empirical ICC shows only the empirical, data-derived, item characteristic curve.

Exp+Empirical ICC plots both the model-expected item characteristic curve, and the empirical, data-derived, curve, together with a confidence band for the empirical around the model curve.

The solid red "model" line is generated by the relevant Rasch model. For a test of dichotomous items, these red curves will be the same for every item with the same rating scale structure. The empirical blue line is constructed from the observed frequencies along the variable, marked by x. The empirical ("x") x- and y-coordinates are the means of the measures and ratings for observations in the interval.

The upper green line (and the lower gray line) are at two model standard errors above (and below) the model "red line", i.e., form a two-sided 95% confidence band. The distance of these lines from the red line is determined by the number of observations in the interval, not by their fit.

Cumulative Probabilities plot the sum of category probabilities. The category median boundaries are the points at which the probability is .5. Click on a line to obtain the category identification.

Conditional Probabilities plots the model ogives for adjacent pairs of categories. Click on a line to obtain the category pairing.

Information Function plots the Fisher statistical information for the item. This is also the model variance of the responses, see RSA p. 100.

Category Information plots the item information partitioned according to the probability of observing the category. Click on a line to obtain the category number.

Display Legend (Hide Legend) displays identification for all lines on the plot

Absolute x-axis displays the curves positioned on the latent variable, rather than relative to the element difficulty. Relative x-axis positions the curves relative to the element difficulty.

Points, Lines, None, Both controls display of the empirical curves.

Smoothing smooths the empirical curves.

Set color changes the color of the currently selected part of the plot.

The graphical display is controlled by:

Adjust or fine-tune minimum or maximum enables you to change the x- and y- scale ranges.

Adjust number of divisions enables you to change the number of x- and y- tick marks and labels.

Empirical interval sets the width of the interval on the latent variable summarized by each x on the empirical lines. Displays only when empirical lines are displayed.

On the plot:

Traceline: You can identify an individual traceline by single-left-clicking on it. Its description will then appear below the plot. Click elsewhere on the plot to remove the selection indicators. You can remove a traceline by double-left-clicking on it. Click on the command button, e.g., "Probability Curves", to return the plot to its initial appearance.

Suggestion: If you need to copy-and-paste several graphs into a document, automate the process with a Windows short-cut macro, such as Autohotkey.

Click on Close Box in upper right corner to close the Graphs menu.

Help for Facets Rasch Measurement Software: www.winsteps.com Author: John Michael Linacre.

 Forum Rasch Measurement Forum to discuss any Rasch-related topic

Rasch Publications
Rasch Measurement Transactions (free, online) Rasch Measurement research papers (free, online) Probabilistic Models for Some Intelligence and Attainment Tests, Georg Rasch Applying the Rasch Model 3rd. Ed., Bond & Fox Best Test Design, Wright & Stone
Rating Scale Analysis, Wright & Masters Introduction to Rasch Measurement, E. Smith & R. Smith Introduction to Many-Facet Rasch Measurement, Thomas Eckes Invariant Measurement with Raters and Rating Scales: Rasch Models for Rater-Mediated Assessments, George Engelhard, Jr. & Stefanie Wind Statistical Analyses for Language Testers, Rita Green
Rasch Models: Foundations, Recent Developments, and Applications, Fischer & Molenaar Journal of Applied Measurement Rasch models for measurement, David Andrich Constructing Measures, Mark Wilson Rasch Analysis in the Human Sciences, Boone, Stave, Yale
in Spanish: Análisis de Rasch para todos, Agustín Tristán Mediciones, Posicionamientos y Diagnósticos Competitivos, Juan Ramón Oreja Rodríguez
Winsteps Tutorials Facets Tutorials Rasch Discussion Groups

Coming Rasch-related Events
Jan. 5 - Feb. 2, 2018, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com
Jan. 10-16, 2018, Wed.-Tues. In-person workshop: Advanced Course in Rasch Measurement Theory and the application of RUMM2030, Perth, Australia (D. Andrich), Announcement
Jan. 17-19, 2018, Wed.-Fri. Rasch Conference: Seventh International Conference on Probabilistic Models for Measurement, Matilda Bay Club, Perth, Australia, Website
Jan. 22-24, 2018, Mon-Wed. In-person workshop: Rasch Measurement for Everybody en español (A. Tristan, Winsteps), San Luis Potosi, Mexico. www.ieia.com.mx
April 10-12, 2018, Tues.-Thurs. Rasch Conference: IOMW, New York, NY, www.iomw.org
April 13-17, 2018, Fri.-Tues. AERA, New York, NY, www.aera.net
May 22 - 24, 2018, Tues.-Thur. EALTA 2018 pre-conference workshop (Introduction to Rasch measurement using WINSTEPS and FACETS, Thomas Eckes & Frank Weiss-Motz), https://ealta2018.testdaf.de
May 25 - June 22, 2018, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com
June 27 - 29, 2018, Wed.-Fri. Measurement at the Crossroads: History, philosophy and sociology of measurement, Paris, France., https://measurement2018.sciencesconf.org
June 29 - July 27, 2018, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Further Topics (E. Smith, Winsteps), www.statistics.com
July 25 - July 27, 2018, Wed.-Fri. Pacific-Rim Objective Measurement Symposium (PROMS), (Preconference workshops July 23-24, 2018) Fudan University, Shanghai, China "Applying Rasch Measurement in Language Assessment and across the Human Sciences" www.promsociety.org
Aug. 10 - Sept. 7, 2018, Fri.-Fri. On-line workshop: Many-Facet Rasch Measurement (E. Smith, Facets), www.statistics.com
Sept. 3 - 6, 2018, Mon.-Thurs. IMEKO World Congress, Belfast, Northern Ireland www.imeko2018.org
Oct. 12 - Nov. 9, 2018, Fri.-Fri. On-line workshop: Practical Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com

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