The amyotrophic lateral sclerosis assessment questionnaire (ALSAQ-40): tests of data quality, score reliability and response rate in a survey of patients

Abstract

Objectives: To evaluate response rate, data quality, and score reliability of the 40 item Amyotrophic Lateral Sclerosis Assessment Questionnaire in a survey of MND patients. Design: A survey of members of the MND Association of the UK, of which half were randomly allocated to receive a survey instrument from the MND Association and the other half allocated to receive the MND Association survey instrument and also the ALSAQ-40 questionnaire. Sample: Five hundred patients were randomly selected from the membership lists of the MND Association, of whom 250 received the MND Association Survey and the ALSAQ-40. Results: Response rate to the survey was 59.2%. Over half of the respondents received the ALSAQ-40. Data for individual items were analysed and found to be distributed across all response categories. All items were found to be highly associated with the scales to which they contribute. Internal consistency reliability of all the five scales of the ALSAQ-40 was also found to be high. Conclusion: Inclusion of the ALSAQ-40 into the survey did not have an adverse effect upon response rates. Furthermore, the ALSAQ-40 was shown to have highly desirable psychometric properties. This paper provides further evidence of the reliability and validity of the measure.

Introduction

Standardised health status instruments are increasingly advocated as key outcome measures in clinical trials and health surveys. As the use of such measures becomes more widespread it is, therefore, essential that the quality of the data gained from them is assessed for quality and appropriateness [1], [2], and, furthermore, that the potential impact of the measures on recruitment is evaluated.

A new disease-specific measure, the 40-item Amyotrophic Lateral Sclerosis Assessment Questionnaire (ALSAQ-40), has recently been introduced [3], which was designed specifically to assess health related quality of life in studies of patients with ALS or other motor neurone diseases. The instrument contains 40 questions that measure five areas of health state: Physical Mobility, Activities of Daily Living and Independence; Eating and Drinking; Communication; and Emotional Functioning. It was developed on the basis of interviews with patients diagnosed with ALS/MND, and in its original developmental formulation contained 78 questions. However, analysis of data, using factor analytic techniques, indicated that 40 items measure the most salient and central concerns of patients. However, to date, the 40-item version of the ALSAQ has been embedded in the original 78-item long form. The study reported here, however, included the ALSAQ-40 in its final 40-item form and permits for the measurement properties of the completed instrument to be assessed.

The ALSAQ-40 was included in a survey on patients assessments of their needs and how well these are met by the Motor Neurone Disease Association (MND Association) in the UK. The purpose of the research reported here was to evaluate the psychometric properties of the instrument and also the extent to which including such a measure in a study may effect response rates. For example, it has been suggested that the longer the questionnaire the lower the response rate [4], [5] and, furthermore, that sensitive questions which may be distressing to respondents, potentially such as those included in the ALSAQ-40, may have adverse effects on subjects willingness to participate in a study. However, on the other hand, it has been suggested that the greater the importance of a study to the individual and the higher the perceived value of the research to society then the more likely that subjects will respond [6]. Thus, in this instance it could be argued that whilst the addition of the ALSAQ-40 may make the MND survey questionnaire longer and potentially more distressing it also adds health status questions that address issues of direct relevance to patients. Furthermore, the results from such a survey may be beneficial to the ALS/MND community as a whole in systematically assessing the impact of the disease upon patients lives. Consequently, in order to determine whether the ALSAQ-40 may adversely effect response rates, a randomised trial design was adopted with half of the patients receiving a copy of the MND Association questionnaire alone and the other half receiving both this and the ALSAQ-40.

The purpose of this study was, therefore, 2-fold: firstly, to determine whether the inclusion of a quality of life questionnaire reduced the response rate, and, secondly, to assess the data completeness, reliability and validity of the measure in a social survey.