Abstract
Objectives: To use statistical procedures, operationalising what is known as item response theory (IRT), to assess the unidimensionality of the 40 item Amyotrophic Lateral Sclerosis Assessment Questionnaire, and consequently to develop a single index figure from the measure. A secondary objective is to compare scores gained on the ALSAQ-40 with a five item short form (the ALSAQ-5).
Methods: Postal survey of patients diagnosed with motor neurone disease (MND) on the MND Associations database. Copies of the ALSAQ-40 and, nested within it, the ALSAQ-5 were completed on two occasions. At time one, the survey contained the ALSAQ-40 and demographic questions. In addition, patients were asked to indicate if they were willing to take part in the follow up. Those who agreed to do so were sent another copy of the questionnaire after a period of three months. Respondents were also asked to indicate how much change they had experienced since baseline on each of the five domains of the questionnaire. Rasch analysis, a form of IRT methodology, was used to determine if the 40 items in the ALSAQ-40 tapped an underlying "latent trait", and were consequently measuring a unidimensional construct. The results from the ALSAQ-40 single index were then compared with those gained from the ALSAQ-5.
Results: Analyses indicated that, at both baseline and follow up, all items on the ALSAQ-40 fitted the Rasch model. Consequently the 40 items were summed to create a single index. Results on this instrument were compared with those gained by summing the five items of the ALSAQ-5. Results on the instruments were found to be highly correlated.
Conclusions: Evidence from the analyses suggests that 40 item ALSAQ does contain a unidimensional scale, and can, therefore be summed to create a single index. Furthermore the ALSAQ-5 closely replicates the results of the patient measure.
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- Fitzpatrick R., Ziebland S., Jenkinson C., Mowat A., Mowat A. Transition questions to assess outcomes in rheumatoid arthritis. Br J Rheumatol. 1993 Sep;32(9):807–811. doi: 10.1093/rheumatology/32.9.807. [DOI] [PubMed] [Google Scholar]
- Haley S. M., McHorney C. A., Ware J. E., Jr Evaluation of the MOS SF-36 physical functioning scale (PF-10): I. Unidimensionality and reproducibility of the Rasch item scale. J Clin Epidemiol. 1994 Jun;47(6):671–684. doi: 10.1016/0895-4356(94)90215-1. [DOI] [PubMed] [Google Scholar]
- Jenkinson C., Fitzpatrick R., Brennan C., Swash M. Evidence for the validity and reliability of the ALS assessment questionnaire: the ALSAQ-40. Amyotroph Lateral Scler Other Motor Neuron Disord. 1999 Dec;1(1):33–40. doi: 10.1080/146608299300080022. [DOI] [PubMed] [Google Scholar]
- Jenkinson C., Fitzpatrick R., Peto V., Greenhall R., Hyman N. The Parkinson's Disease Questionnaire (PDQ-39): development and validation of a Parkinson's disease summary index score. Age Ageing. 1997 Sep;26(5):353–357. doi: 10.1093/ageing/26.5.353. [DOI] [PubMed] [Google Scholar]
- Jenkinson C., Fitzpatrick R. Reduced item set for the amyotrophic lateral sclerosis assessment questionnaire: development and validation of the ALSAQ-5. J Neurol Neurosurg Psychiatry. 2001 Jan;70(1):70–73. doi: 10.1136/jnnp.70.1.70. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Jenkinson C., Levvy G., Fitzpatrick R., Garratt A. The amyotrophic lateral sclerosis assessment questionnaire (ALSAQ-40): tests of data quality, score reliability and response rate in a survey of patients. J Neurol Sci. 2000 Nov 1;180(1-2):94–100. doi: 10.1016/s0022-510x(00)00420-2. [DOI] [PubMed] [Google Scholar]
- Juniper E. F., Guyatt G. H., Willan A., Griffith L. E. Determining a minimal important change in a disease-specific Quality of Life Questionnaire. J Clin Epidemiol. 1994 Jan;47(1):81–87. doi: 10.1016/0895-4356(94)90036-1. [DOI] [PubMed] [Google Scholar]
- Kükdeveci A. A., Yavuzer G., Tennant A., Süldür N., Sonel B., Arasil T. Adaptation of the modified Barthel Index for use in physical medicine and rehabilitation in Turkey. Scand J Rehabil Med. 2000 Jun;32(2):87–92. [PubMed] [Google Scholar]
- Linacre J. M. FIM levels as ordinal categories. J Outcome Meas. 2000;4(2):616–633. [PubMed] [Google Scholar]
- Scheltens P. Early diagnosis of dementia: neuroimaging. J Neurol. 1999 Jan;246(1):16–20. doi: 10.1007/s004150050300. [DOI] [PubMed] [Google Scholar]
- Tsuji T., Liu M., Sonoda S., Domen K., Chino N. The stroke impairment assessment set: its internal consistency and predictive validity. Arch Phys Med Rehabil. 2000 Jul;81(7):863–868. doi: 10.1053/apmr.2000.6275. [DOI] [PubMed] [Google Scholar]
- Wright B. D., Linacre J. M., Smith R. M., Heinemann A. W., Granger C. V. FIM measurement properties and Rasch model details. Scand J Rehabil Med. 1997 Dec;29(4):267–272. [PubMed] [Google Scholar]