DIF= columns within person label for Table 30 = $S1W1

DIF= specifies the part of the person label which is to be used for classifying persons in order to identify Differential Item Function (DIF) - uniform or non-uniform - using the column selection rules. See also DIF Table and DIF and DPF considerations.

 

DIF= *file name

file containing details

DIF= *

in-line list

DIF= $S1W1

field in person label. DIF fields must be inside the person label defined by NAME1= and NAMELENGTH=

DIF= MA2

person ability levels for non-uniform DIF: MA2 splits at the middle of the value value.range

DIF=  $S1W1 + MA2

person classes or groups

DIF= ?

open browser for file

 

DIF= location is usually column number within person label field. DIF=1 means "DIF selection character is first character of person label."

 

Example 1: Columns 18-20 of the person label (in columns 118-120 of the data record) contain a district code:

 NAME1=101  ; person label starts in column 101

 NAMELENGTH = 20 ; person label must include all the DIF codes

 DIF = $S18W3  ; district starts in column 18 of person label with a width of 3

or

 @district = 18W3 ; district starts in column 18 of person label with a width of 3

 DIF = @district  ; DIF classifier

 tfile=*

 30   Table 30 for the DIF report (or use Output Tables menu)

 *

 

Example 2: DIF by Gender+Grade: Column 1 of the person labels contains gender (M or F) and Columns 7-8 contain grade level (K-12).

 DIF = 1W1 + 7W2

 

Example 3: I have tab-separated data and my DIF indicator is in a separate field from the Person label.

Solution: for the DIF analysis, do a separate run of Winsteps. At the "Extra Specifications" prompt:

NAME1=(location of DIF indicator)

DIF=$S1W1

 

Example 4: Columns 18-20 of the person label (in columns 118-120 of the data record) contain a district code. Column 21 of the person label (in column 121 of the data record) has a gender code. Three independent DIF analyses are needed: district, gender, district+gender

NAME1=101  ; person label starts in column 101

NAMELENGTH = 21 ; person label must include all the DIF codes

DIF = *

$S18W3  ; start in person label column 18 with a width of 3 - district

$S21W1  ; start in person label column 21 with a width of 1 - gender

$S18W3+ $S21W1  ; DIF by district+gender

*

tfile=*

30   Table 30 for the DIF report (or use Output Tables menu)

*

 

Example 5: An investigation of non-uniform DIF with high-low ability classification for the KCT data.

; action the following with the Specification pull-down menu

@SEX = $S9W1 ; the sex of participants is in column 9 of the person label

DIF = @SEX + MA2 ; look for non-uniform DIF (gender + two ability strata): MA2

PSUBTOT = @SEX + MA2 ; summary statistics by gender and ability strata

Tfile=*   ; This is more easily actioned through the Output Tables Menu

30   ; Table 30 - DIF report

28   ; Table 28 - Person subtotals for DIF classifications

*

 

Table 30: DIF specification is: DIF=@SEX+MA2

+-----------------------------------------------------------------------------------------+

| KID     DIF   DIF   KID     DIF   DIF      DIF    JOINT          TAP                    |

| CLASS MEASURE S.E.  CLASS MEASURE S.E.  CONTRAST  S.E.   t  d.f. Number  Name           |

|-----------------------------------------------------------------------------------------|

| F1     -1.86  1.09  M1     -4.54  1.15      2.68  1.59  1.69   8      6 6= 3-4-1        |

 

Table 28: Subtotal specification is: PSUBTOTAL=@SEX+MA2

+---------------------------------------------------------+

| KID     MEAN     S.E.  OBSERVED  MEDIAN   REAL          |

| COUNT  MEASURE   MEAN    P.SD          SEPARATION  CODE |

|---------------------------------------------------------|

|      4   -2.08     .90     .89             .00     F1   | <- Non-extreme

|      6   -2.82     .41     .91   -2.86     .32     M1   |

 

Example 6: With Example0.txt (the Liking for Science rating scale data) you want to see if any items were biased against names starting with any letter of the alphabet, then:

 

run example0.txt

request the DIF Table (Table 30) from the Output Tables menu

specify: $S1W1

a DIF table is produced.

 

The equivalent DIF specification is: DIF=$S1W1

 

Positive DIF size is higher ACT difficulty measure

+------------------------------------------------------------------------------------+

| KID     DIF   DIF   KID     DIF   DIF      DIF    JOINT          ACT               |

| CLASS MEASURE S.E.  CLASS MEASURE S.E.  CONTRAST  S.E.   t  d.f. Number  Name      |

|------------------------------------------------------------------------------------|

| R       -.06   .54  W        .89> 2.05      -.95  2.12  -.45   8     1 WATCH BIRDS |

| R       -.06   .54  L       -.65   .75       .59   .92   .64  12     1 WATCH BIRDS |

| R       -.06   .54  S       -.42   .57       .36   .78   .46  18     1 WATCH BIRDS |

| R       -.06   .54  H      -1.63  1.13      1.57  1.25  1.26  11     1 WATCH BIRDS |

| R       -.06   .54  D        .12   .86      -.18  1.01  -.18  11     1 WATCH BIRDS |

.......

 

Example 7: The DIF demographic column is not part of the person label. Use the FORMAT= instruction to rearrange the record.

Was:

 0        1         2         3

 123456789012345678901234567890

 AxxxxxxxxxxxxxxxxxxxBCyyyyyyyy ; original record layout

 ITEM1=2

 NI=19  ; the x's

 NAME1=21 ; starts with B

 

To move column 1 after column 21 with XWIDE=1:

 xxxxxxxxxxxxxxxxxxxBACyyyyyyyy ; after internal reformatting

 FORMAT = (T2,20A,T1,1A,T22,100A)

 ITEM1 = 1 ; references position in the reformatted record.

 NI = 19 ; the x's

 NAME1 = 20 ; starts with B - references position in the reformatted record. 

 DIF = S2W1 ; code A

 

The first reformatted record is shown on your screen so you can check that it is how you want it.

 

Example 8: We only want DIF between person classification groups A and B, not the other person groups. Classification group code is in column 3 of the person label.

In the Specification pull down menu

PSELECT=??{AB}

Output Table menu: Table 30.


Help for Winsteps Rasch Measurement and Rasch Analysis Software: www.winsteps.com. Author: John Michael Linacre

Facets Rasch measurement software. Buy for $149. & site licenses. Freeware student/evaluation Minifac download
Winsteps Rasch measurement software. Buy for $149. & site licenses. Freeware student/evaluation Ministep download

Rasch Books and Publications
Invariant Measurement: Using Rasch Models in the Social, Behavioral, and Health Sciences, 2nd Edn, 2024 George Engelhard, Jr. & Jue Wang Applying the Rasch Model (Winsteps, Facets) 4th Ed., Bond, Yan, Heene Advances in Rasch Analyses in the Human Sciences (Winsteps, Facets) 1st Ed., Boone, Staver Advances in Applications of Rasch Measurement in Science Education, X. Liu & W. J. Boone Rasch Analysis in the Human Sciences (Winsteps) Boone, Staver, Yale
Introduction to Many-Facet Rasch Measurement (Facets), Thomas Eckes Statistical Analyses for Language Testers (Facets), Rita Green Invariant Measurement with Raters and Rating Scales: Rasch Models for Rater-Mediated Assessments (Facets), George Engelhard, Jr. & Stefanie Wind Aplicação do Modelo de Rasch (Português), de Bond, Trevor G., Fox, Christine M Appliquer le modèle de Rasch: Défis et pistes de solution (Winsteps) E. Dionne, S. Béland
Exploring Rating Scale Functioning for Survey Research (R, Facets), Stefanie Wind Rasch Measurement: Applications, Khine Winsteps Tutorials - free
Facets Tutorials - free
Many-Facet Rasch Measurement (Facets) - free, J.M. Linacre Fairness, Justice and Language Assessment (Winsteps, Facets), McNamara, Knoch, Fan
Other Rasch-Related Resources: Rasch Measurement YouTube Channel
Rasch Measurement Transactions & Rasch Measurement research papers - free An Introduction to the Rasch Model with Examples in R (eRm, etc.), Debelak, Strobl, Zeigenfuse Rasch Measurement Theory Analysis in R, Wind, Hua Applying the Rasch Model in Social Sciences Using R, Lamprianou El modelo métrico de Rasch: Fundamentación, implementación e interpretación de la medida en ciencias sociales (Spanish Edition), Manuel González-Montesinos M.
Rasch Models: Foundations, Recent Developments, and Applications, Fischer & Molenaar Probabilistic Models for Some Intelligence and Attainment Tests, Georg Rasch Rasch Models for Measurement, David Andrich Constructing Measures, Mark Wilson Best Test Design - free, Wright & Stone
Rating Scale Analysis - free, Wright & Masters
Virtual Standard Setting: Setting Cut Scores, Charalambos Kollias Diseño de Mejores Pruebas - free, Spanish Best Test Design A Course in Rasch Measurement Theory, Andrich, Marais Rasch Models in Health, Christensen, Kreiner, Mesba Multivariate and Mixture Distribution Rasch Models, von Davier, Carstensen
As an Amazon Associate I earn from qualifying purchases. This does not change what you pay.

facebook Forum: Rasch Measurement Forum to discuss any Rasch-related topic

To receive News Emails about Winsteps and Facets by subscribing to the Winsteps.com email list,
enter your email address here:

I want to Subscribe: & click below
I want to Unsubscribe: & click below

Please set your SPAM filter to accept emails from Winsteps.com
The Winsteps.com email list is only used to email information about Winsteps, Facets and associated Rasch Measurement activities. Your email address is not shared with third-parties. Every email sent from the list includes the option to unsubscribe.

Questions, Suggestions? Want to update Winsteps or Facets? Please email Mike Linacre, author of Winsteps mike@winsteps.com


State-of-the-art : single-user and site licenses : free student/evaluation versions : download immediately : instructional PDFs : user forum : assistance by email : bugs fixed fast : free update eligibility : backwards compatible : money back if not satisfied
 
Rasch, Winsteps, Facets online Tutorials


 

 
Coming Rasch-related Events: Winsteps and Facets
Oct 21 - 22 2024, Mon.-Tues. In person workshop: Facets and Winsteps in expert judgement test validity - UNAM (México) y Universidad Católica de Colombia. capardo@ucatolica.edu.co, benildegar@gmail.com
Oct. 4 - Nov. 8, 2024, Fri.-Fri. On-line workshop: Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com
Jan. 17 - Feb. 21, 2025, Fri.-Fri. On-line workshop: Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com
May 16 - June 20, 2025, Fri.-Fri. On-line workshop: Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com
June 20 - July 18, 2025, Fri.-Fri. On-line workshop: Rasch Measurement - Further Topics (E. Smith, Facets), www.statistics.com
Oct. 3 - Nov. 7, 2025, Fri.-Fri. On-line workshop: Rasch Measurement - Core Topics (E. Smith, Winsteps), www.statistics.com

 

 

Our current URL is www.winsteps.com

Winsteps® is a registered trademark