What makes a measurement instrument valid and reliable?

High quality instruments are useful tools for clinical and research purposes. To determine whether an instrument has high quality, measurement properties such as reliability and validity need to be assessed, using standardised criteria. This paper discusses these quality domains and measurement properties using the standardised criteria that were recently published by the COSMIN group. Examples are given of studies evaluating the measurement properties of instruments frequently used in trauma. This paper presents a helpful tool for readers who want to evaluate or assess the quality of a measurement instrument on reliability and validity.     

Methodological challenges in quality of life research among Turkish and Moroccan ethnic minority cancer patients: translation,recruitment and ethical issues

The large population of first generation Turkish and Moroccan immigrants who moved to Western Europe in the 1960s and 1970s is now reaching an age at which the incidence of chronic diseases, including cancer, rises sharply. To date, little attention has been paid to the health-related quality of life (HRQOL) of these ethnic minority groups, primarily due to the paucity of well translated and validated measures, but also because of a range of methodological and logistical barriers. The primary objective of this paper is to describe the methodological challenges in conducting HRQOL research among these patient populations, based on experience gained in a project in which four widely used HRQOL questionnaires were translated into Turkish, Moroccan-Arabic and Tarifit, and administered to a sample of 90 Turkish and 79 Moroccan cancer patients in the Netherlands. Problems encountered in translating and administering the questionnaires included achieving semantic equivalence (use of loanwords), use of numerical rating scales, lengthy questions and response scales, and culturally sensitive and/or inappropriate questions. Privacy laws that prohibit hospitals from registering the ethnicity of patients hampered efficient identification of eligible patients. Recruiting patients to studies is often difficult due to low literacy levels, lack of familiarity with and distrust of research, concerns about immigration status, and inaccurate or missing contact information. This can lead to lower response rates than is the case with the population of Dutch cancer patients. Additional ethical issues that arise in such studies concern patients’ problems with communicating with their health care providers, their lack of understanding of their diagnosis, treatment and prognosis, and the potential role conflict experienced by bilingual research assistants who may wish or be asked to intervene on the patients’ behalf. Practical approaches to resolving these issues are presented.     

Determinants of adherence to heart failure medication: a systematic literature review

A systematic literature review was conducted to summarize the existing evidence on presumed determinants of heart failure (HF) medication adherence. The aim was to assess the evidence and provide directions for future medication adherence interventions for HF patients. Based on a search in relevant databases and a quality assessment, eleven articles were included in the review. A best evidence synthesis was used to combine the results of presumed determinants that were found more than once in the literature. Results were classified according the World Health Organization’s (WHO) multidimensional adherence model. Results demonstrated a relationship between having been institutionalized in the past (including hospitalizations and nursing home visits) and higher adherence levels. This finding is related to the healthcare system dimension of the WHO model. The presumed determinants related to the other dimensions, such as social and economic factors, condition-related, therapy-related, and patient-related factors of the multidimensional adherence model all had inconsistent evidence. However, there was also an indication that patients’ educational level and the number of healthcare professionals they have visited are not related to higher adherence levels. Based on the current review, HF patients who have been institutionalized in the past are more adherent to HF medication. Many other presumed determinants were investigated, but displayed inconsistent evidence. Due to the lack of evidence, it was not possible to make recommendations for future interventions.     

Self-report fatigue questionnaires in multiple sclerosis, Parkinson’s disease and stroke: a systematic review of measurement properties

Purpose

To critically appraise, compare and summarize the measurement properties of self-report fatigue questionnaires validated in patients with multiple sclerosis (MS), Parkinson??s disease (PD) or stroke.

Methods

MEDLINE, EMBASE, PsycINFO, CINAHL and SPORTdiscus were searched. The COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) checklist was used to assess the methodological quality of studies. A qualitative data synthesis was performed to rate the measurement properties for each questionnaire.

Results

Thirty-eight studies out of 5,336 records met the inclusion criteria, evaluating 31 questionnaires. Moderate evidence was found for adequate internal consistency and structural validity of the Fatigue Scale for Motor and Cognitive functions (FSMC) and for adequate reliability and structural validity of the Unidimensional Fatigue Impact Scale (U-FIS) in MS.

Conclusions

We recommend the FSMC and U-FIS in MS. The Functional Assessment of Chronic Illness Therapy Fatigue subscale (FACIT-F) and Fatigue Severity Scale (FSS) show promise in PD, and the Profile of Mood States Fatigue subscale (POMS-F) for stroke. Future studies should focus on measurement error, responsiveness and interpretability. Studies should also put emphasis on providing input for the theoretical construct of fatigue, allowing the development of questionnaires that reflect generic and disease-specific symptoms of fatigue.     

Relation between injected volume and optical parameters in refilled isolated porcine lenses

PURPOSE: This study was performed to elucidate the correlation between added lens refill material and enhanced lens power as well as the correlation between lens refilling volume and accommodative amplitude as determined by equatorial stretching of ex vivo refilled pigs' lenses. METHODS: Nine porcine lenses were refilled with increasing amounts of silicone oil. After each refill step, the lens power, the lens power change, and the lens thickness were measured both in the relaxed state and with a 3-mm larger ciliary body diameter. In addition, the spherical aberration of the refilled lenses was also quantified. RESULTS: Injection of 0.04 mL silicone material into the relaxed lens enhanced the lens power by 1 D. A 0.54-mm increase of the lens thickness in relaxed lenses added 1 D to the lens power. Increasing the lens refilling volume decreased the lens power changes measured at 3-mm ciliary body stretch. Spherical aberration was positive in the refilled lenses and increased with increasing lens refilling volume. CONCLUSION: The correlation found between the refilling volume and the lens power (0.04 mL D(-1)), as well as the correlation between the lens thickness and the lens power (0.54 mm D(-1)), might be important factors to be controlled in conjunction with surgery, as these also determine the lens power in the presence of this refill material. An increasing lens filling volume is associated with decreasing accommodative amplitude. The positive spherical aberration of refilled porcine lenses presents a sharp contrast to the negative aberration of natural pigs' lenses. Different lens contours and the transition from a gradient to a homogeneous refractive index might be responsible for this change in spherical aberration.     

Understanding Ferguson's δ: time to say good-bye?

A critique of Hankins, M: 'How discriminating are discriminative instruments?' Health and Quality of Life Outcomes 2008, 6:36.