IRT or Rasch–what can and cannot be done? · 2019-06-27 · 2019-06-25 1 [email protected]...

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[email protected] 2019-06-12 PM-Health

IRT or Rasch – what can and cannot be done?

L R Pendrill1, and the EMPIR NeuroMet 15HLT04 consortium

1RI.SE Research Institutes in Sweden, Metrology, Eklandagatan 86, 41261 Göteborg (SE), phone:+46 767 88 54 44, mailto:[email protected]

WORKSHOP


35 arthritis patients have been through rehabilitation therapy. Their admission to therapy and discharge from therapy measures are to be compared. They have been rated on the 13 mobility items of the Functional Independence Measure (FIMTM).

Each item has seven levels.

At admission, the patients could not perform at the higher levels. At discharge, all patients had surpassed the lower levels (Data courtesy of C.V. Granger & B. Hamilton, ADS).

EXAM12

1 0% Independent2 25% Independent3 50% Independent4 75% Independent5 Supervision6 Device7 Independent

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[email protected] 2019-06-12 PM-Health W P Fisher Jr. 1999

)Difficulty(d

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Score, x1 0% Independent2 25% Independent3 50% Independent4 75% Independent5 Supervision6 Device7 Independent


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Most able

Leastable

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DifficultEasy


Most able

Leastable

Most difficult

Leastdifficult

! "#$%$&'

( )$**$+,%&'k = 2

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!"# =1&'( )*+,-

./0"+,#CTT mean of

response x

2(!"#) =1

&'( ) &'( − 1 )*+,-

./0"+,# − !"#6u(CTT mean of

response x)

k = 1

Score, x1 0% Independent2 25% Independent3 50% Independent4 75% Independent5 Supervision6 Device7 Independent

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!"# =1&'( )*+,-

./0"+,#CTT mean of

response x

Difficult

Easy

k = 1


!",$,% ='∑)*+, -./01,)

∑%2341 '∑)*+, -./01,)

Score residual, y 5",$ = 6",$ − 8",$

8",$ = 9%23

41: ; !",$,%Expected mean, E, of

response x

Graphs: Test Characteristic Curve

6",$

8",$

5",$

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!"#!$_&'()_*+ =2 . / 0 −

/"23 −

23

55 = 6

7.89:;<

=/

Molton: “Both statistics … require a lot of meditation and incense. For useful explanations, refer to: http://www.rasch.org/rmt/rmt162f.htm”.

0 = >?6 = @ABC

9:;

DA6

EA,?,G =H∑JKL

M NO<PQ,J

∑GBRSQ H∑JKL

M NO<PQ,J

Score residual, y DA,? = TA,? − UA,?

UA,? = @GBR

SQ

V . EA,?,GExpected mean, E, of

response x

[email protected] 2019-06-12 PM-Healthk = 2

Physical disability

http://www.rasch.org/rmt/rmt162f.htm

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Physical disability

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!. #$%&'# #()*+,'(-./01 = 7 − !. #$%&'# #()*+,'(

Physical disability

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Acquiescence

!"#$$%"" ='()*

1 + '()*

”Agreement regardless of item content∆. = / 0 .; / < 0

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Difficult

Easy

Difficulty

Physical disability


DifficultEasy

Physical disability

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Physical disability


Fit residual

!"#$$%"" ='()*

1 + '()*

- =.!"#$$%""./

='01 ()*

1 + ' ()* 0−

' ()*

1 + ' ()*

34,6 = 74,6 − 84,6

Response Sensitivity

9:;<=_?@=A_BC =

2 1EF −

EGHI −

23

K

L′6,*0= L6 −

.!"#$$%""./

1 ./0

= L60 − 2 1

.!"#$$%""./

1 ./ 1 L6 +.!"#$$%""./

1 ./0

Changedstimulus

F = L60 = N

4OP

QRS

34,60

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Acquiesence, τ < 0Importancerescaling, τ > 0

[email protected] 2019-06-12 PM-Health W P Fisher Jr. 1999

)Difficulty(d

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Metrologicalreferences

Difficulty

Mass

Tasks

)(Difficultyd

Physical disability


Acknowledgments

Work performed as part of 15HLT04 NeuroMet project, European Metrology Programme for Innovation & Research (Horizon 2020), jointly funded by EMRP participating countries within EURAMET (www.euramet.org) and European Union.

Thanks are due, particularly, to: • Members of the EMPIR NeuroMet consortium • Jeanette Melin, RISE Metrology Göteborg Sweden• Stefan Cano, Modus Outcomes, Boston (USA) & Stotford UK• William P. Fisher, Jr., Ph.D., Research Associate, BEAR Center, Graduate

School of Education, University of California, Berkeley, CA (USA) & Principal, LivingCapitalMetrics Consulting

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NeuroMET: Innovative measurements for improved diagnosis and management of neurodegenerative diseases

Acknowledgments

This project has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme

NeuroMET : www.lgcgroup.com/EMPIR-neuromet


EURAMET’s Research Programmes

IRT or Rasch–what can and cannot be done? · 2019-06-27 · 2019-06-25 1 [email protected]...

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