TY - JOUR
T1 - Validating the 28-tender joint count using item response theory
AU - Tjin-Kam-Jet-Siemons, Liseth
AU - ten Klooster, Peter M.
AU - Taal, Erik
AU - Kuper, I.H.
AU - van Riel, Piet L.C.M.
AU - van de Laar, Mart A F J
AU - Glas, Cornelis A.W.
PY - 2011
Y1 - 2011
N2 - Objective:
To examine the construct validity of the 28-tender joint count (TJC-28) using item response theory (IRT)-based methods.
Methods:
A total of 457 patients with early stage rheumatoid arthritis (RA) were included. Internal construct validity of the TJC-28 was evaluated by determining whether the TJC-28 fit a 2-measure logistic IRT model. As well, we tested whether the discrimination and difficulty parameters of the joints properly reflected the known left-right symmetry of joint involvement. External validity was evaluated by correlations with other established measures of disease activity, including pain, disability, general health, erythrocyte sedimentation rate (ESR), and the 28-swollen joint count.
Results:
The TJC-28 showed a good fit with the 2-parameter logistic model, with no relevant differential item functioning across sex, age, and time and with excellent reliability. The 28 joints covered a reasonable range of disease activity, even though they were mainly targeted at patients with moderate or high disease activity levels. The joint parameters reflected the left-right symmetry of joint involvement for all pairs of joints except one. All disease activity measures, except ESR, were significantly correlated with the TJC-28. Most correlations were of the expected magnitude.
Conclusion:
The TJC-28 showed good internal and acceptable external construct validity for patients with early-stage RA. The IRT analyses did point to some potential limitations of the instrument, a major problem being its limited measurement range. Future research should examine whether instrument modifications might lead to a more robust assessment of disease activity in patients with RA.
AB - Objective:
To examine the construct validity of the 28-tender joint count (TJC-28) using item response theory (IRT)-based methods.
Methods:
A total of 457 patients with early stage rheumatoid arthritis (RA) were included. Internal construct validity of the TJC-28 was evaluated by determining whether the TJC-28 fit a 2-measure logistic IRT model. As well, we tested whether the discrimination and difficulty parameters of the joints properly reflected the known left-right symmetry of joint involvement. External validity was evaluated by correlations with other established measures of disease activity, including pain, disability, general health, erythrocyte sedimentation rate (ESR), and the 28-swollen joint count.
Results:
The TJC-28 showed a good fit with the 2-parameter logistic model, with no relevant differential item functioning across sex, age, and time and with excellent reliability. The 28 joints covered a reasonable range of disease activity, even though they were mainly targeted at patients with moderate or high disease activity levels. The joint parameters reflected the left-right symmetry of joint involvement for all pairs of joints except one. All disease activity measures, except ESR, were significantly correlated with the TJC-28. Most correlations were of the expected magnitude.
Conclusion:
The TJC-28 showed good internal and acceptable external construct validity for patients with early-stage RA. The IRT analyses did point to some potential limitations of the instrument, a major problem being its limited measurement range. Future research should examine whether instrument modifications might lead to a more robust assessment of disease activity in patients with RA.
KW - IR-82754
KW - METIS-281285
U2 - 10.3899/jrheum.110436
DO - 10.3899/jrheum.110436
M3 - Article
VL - 38
SP - 2557
EP - 2564
JO - Journal of rheumatology
JF - Journal of rheumatology
SN - 0315-162X
IS - 12
ER -