Table 13 Bias report 
This Table compares the local (biased?) measure of one element with its measure from the main analysis. Zscore=, Bias=, Xtreme=, Arrange= and Juxtapose= control this Table.
++
Observd Expctd Observd ObsExp Bias Model Infit Outfit Senior scientists Junior Scientis 
 Score Score Count Average Size S.E. t d.f. Prob.  MnSq MnSq  Sq N Senior sc measr N Junior measr 
+++
 4.2 7.91 1.5 2.47 1.00 .61 1.63 1 .3496  .6 .6  14 2 Brahe .21 5 Edward .34 
+++
 7.3 7.25 1.5 .01 .01 .56 .03  .6 .6  Mean (Count: 21) 
 2.1 1.25 .0 .98 .42 .03 .72  .4 .4  S.D. (Population) 
 2.1 1.28 .0 1.00 .43 .03 .73  .4 .4  S.D. (Sample) 
++
Fixed (all = 0) chisquare: 10.8 d.f.: 21 significance (probability): .97

The column headings mean:
Observd Score = raw score of the estimable responses involving these elements simultaneously, as observed in the data file.
Expctd Score = expected score based on the measures from the main analysis.
Observd Count = number of estimable responses involving these elements simultaneously.
ObsExp Average = observed score less the expected score divided by observed count, the bias in terms of the response metric. For rater behavior, look at the "ObsExp Average". If this is positive, then the rater is more lenient than expected in this situation. If this is negative, then the rater is more severe than expected.
Bias Size = Size of bias measure in logodds units, logits, relative to overall measures. Only large or significant biases are listed greater than Zscore=. For clarification, compare the ranking of the ObsExp Average with that of the Bias Size. In this case, larger observed scores correspond to higher Bias sizes, i.e., higher abilities, higher leniencies, higher easiness. The sign of the report bias is controlled by Bias=
For (measure+bias), add Bias Size to the element "measr", or subtract Bias Size from "measr". Addition for persons that are locally more able. Subtraction for items that are locally more difficult. Look at the "ObsExp Average".
Model Error = standard error of the bias estimate.
t = Student's tstatistic testing the hypothesis "There is no bias apart from measurement error". The "Obsvd Count"2 approximates the degrees of freedom of the tstatistic. With many observations, the tstatistic approximates a normal distribution with mean = 0, S.D. = 1, i.e., a zscore. The tstatistic is the report of a test of the statistical significance of the size of the bias. In this table, statistically significant bias indicates that the difference between the element measure for this interaction and the overall element measure is greater than the difference we would expect to see by chance.
Infit MnSq and Outfit MnSq = Does the bias explain all the misfit or is there also another source of misfit? Values are expected to be less than 1.0 because the bias is explaining some of the overall misfit. These statistics do not report the fit of the bias terms. In effect, we are deliberately overparameterizing the statistical model. Consequently we expect the meansquares to be less than 1.0 (by an unknown amount). The reported meansquares indicate how much misfit remains after the interactions are estimated. The reported meansquares do not have the usual statistical properties of meansquares (chisquares) and so their statistical significance (Zstd) is unknown. The purpose of the meansquare fit statistics is to help you determine whether the misfit in the data is explained by the bias or is due to other causes.
For each facet entering into the bias calculation:
Sq = a sequence number used to reference the bias term  useful for referring to a specific line in this Table.
N = element number with Facet. Only elements with nonextreme measures are included.
Senior Sc = Name of facet: elements listed below
measr = Measure of element from main analysis.
In the summary statistics,
Count = the number of modeled bias terms found in the data.
S.D. (Population) = the standard deviation if this sample is the whole population
S.D. (Sample) = the standard deviation if this sample is a random sample from the whole population
Fixed (all=0) chisquare = A test of the "fixed effect" hypothesis: "Can this set of interactions be regarded as sharing the same measure of approximately 0.0 after allowing for measurement error?" The chisquare value and degrees of freedom (d.f.) are shown. The significance is the probability that this "fixed" hypothesis is the case. This is not a test of "Can these interactions be disregarded?" Individual interactions may be large and significant. For instance, one bad tire in a production run of 1000 tires may not indicate a "statistically significant" problem in the production process, but I still don't want it on my car!
The chisquares and ttests evaluate hypothesis tests.
Think of driving along the road.
A.) Is this road surface generally OK?
Answer: (in another dataset): Fixed (all = 0) chisquare: 20 d.f.: 21 significance (probability): .5
So we can't reject the hypothesis that the road surface is generally OK.
B.) Are there any potholes we should avoid (even if the road is generally OK)?
Answer: the ttest Prob.  in the Table above BraheDavid p=.02. This is a "pothole"!
Example using earlier Facets output:
The observed score is 40. The expected score is 33.6. There are 9 observations. So, on average, Group 3 is being rated 0.71 scorepoints higher than expected by Judge J4. This corresponds to a change in judge severity of .70 logits = less severe. The standard error is .34 logits. So the Zscore (ttest with infinite d.f.) is 2.04. The rater is significantly less severe (more lenient) at the .05 level (doublesided). If we want to report this as a change in group ability of +.71 logits, set Bias=Positive.
Help for Facets Rasch Measurement Software: www.winsteps.com Author: John Michael Linacre.
For more information, contact info@winsteps.com or use the Contact Form
Facets Rasch measurement software.
Buy for $149. & site licenses.
Freeware student/evaluation download Winsteps Rasch measurement software. Buy for $149. & site licenses. Freeware student/evaluation download 

Stateoftheart : singleuser 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 

Forum  Rasch Measurement Forum to discuss any Raschrelated topic 
Click here to add your email address to the Winsteps and Facets email list for notifications.
Click here to ask a question or make a suggestion about Winsteps and Facets software.
Coming Raschrelated Events  

Jan. 5  Feb. 2, 2018, Fri.Fri.  Online workshop: Practical Rasch Measurement  Core Topics (E. Smith, Winsteps), www.statistics.com 
Jan. 1016, 2018, Wed.Tues.  Inperson workshop: Advanced Course in Rasch Measurement Theory and the application of RUMM2030, Perth, Australia (D. Andrich), Announcement 
Jan. 1719, 2018, Wed.Fri.  Rasch Conference: Seventh International Conference on Probabilistic Models for Measurement, Matilda Bay Club, Perth, Australia, Website 
Jan. 2224, 2018, MonWed.  Inperson workshop: Rasch Measurement for Everybody en español (A. Tristan, Winsteps), San Luis Potosi, Mexico. www.ieia.com.mx 
April 1012, 2018, Tues.Thurs.  Rasch Conference: IOMW, New York, NY, www.iomw.org 
April 1317, 2018, Fri.Tues.  AERA, New York, NY, www.aera.net 
May 22  24, 2018, Tues.Thur.  EALTA 2018 preconference workshop (Introduction to Rasch measurement using WINSTEPS and FACETS, Thomas Eckes & Frank WeissMotz), https://ealta2018.testdaf.de 
May 25  June 22, 2018, Fri.Fri.  Online 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.  Online workshop: Practical Rasch Measurement  Further Topics (E. Smith, Winsteps), www.statistics.com 
July 25  July 27, 2018, Wed.Fri.  PacificRim Objective Measurement Symposium (PROMS), (Preconference workshops July 2324, 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.  Online workshop: ManyFacet 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.  Online workshop: Practical Rasch Measurement  Core Topics (E. Smith, Winsteps), www.statistics.com 
Our current URL is www.winsteps.com
Winsteps^{®} is a registered trademark
Concerned about aches, pains, youthfulness? Mike and Jenny suggest Liquid Biocell 
