Many guidance documents describe the criteria by which measurement tools should be evaluated (Finch et al., 2002
; Revicki, 2007
; Schoneveld et al., 2009
; Baker et al., 2011
) and funding agencies have published guidelines outlining the scientific requirements for patient-reported outcomes (PROs) and health-related quality of life (HR-QOL) measures (Scientific Advisory Committee of the Medical Outcome Trust (SAC MOT), 2002
; United States Food and Drug Administration (USFDA) 2006
). Despite their focus, these latter guidelines are pertinent to all measurement tools, including those of fine motor skills in people with tremor disorders.
A crucial first step in identifying and selecting an appropriate measurement tool is to define the purpose for which the measurement will be used. This helps clarify the reason for obtaining the measurement, identify the patient population being targeted, determine the setting in which the measurement tool will be used, and specify the aspect(s) of upper extremity fine motor skills that need(s) to be measured. Only when the measurement purpose has been clearly defined is it possible to properly evaluate and select the most appropriate measurement tool.
Table presents key attributes that are used to describe the qualities and features of measurement tools (Baker et al., 2011
; Finch et al., 2002
; Scientific Advisory Committee of the Medical Outcome Trust (SAC MOT), 2002
; United States Food and Drug Administration (USFDA), 2006
). It includes a brief definition of each attribute and questions for consideration when selecting a tool to measure fine motor skills for people with tremor disorders. Table A presents attributes that apply to all measurement tools and includes several familiar terms, a few of which will be highlighted here. The conceptual and measurement model
and scaling assumptions
of a tool are closely related to validity
. However, an explicit definition of the construct being measured is not always provided by the tool developers, or the definition describes the items of the tool rather than the construct it intends to measure. It is therefore important to ensure the measurement tool or one of its sub-scales focuses specifically on the construct of fine motor skills. Responsiveness
is an important attribute when tracking disease progression or assessing the effectiveness of an intervention aimed at reducing tremor severity and improving hand function. For a tool to be responsive it must generate rigorous scientific measurements; unfortunately this is not always the case in measures of activity limitations (Hobart et al., 2007
). When a measurement tool generates ordered scores, it may be assumed that increments in score are equivalent across the range of possible scores, i.e., that it is a linear measure. However, the nature of this relationship is often not known, which hampers the interpretation of scores. Modern psychometric methods such as Rasch analysis and Item Response Theory can improve a tool’s properties and render them rigorous scientific measurements (Hambleton and Swaminathan, 1985
; Andrich, 1988
); the use of such methods is still not widespread in clinical research.
Attributes of measurement tools.
Fine motor skills encompass a wide range of simple and complex tasks with different functional and physiological requirements (McPhee, 1987
; Wiesendanger and Serrien, 2001
; Jones and Lederman, 2006
; Kus et al., 2011
). Table B presents attributes that are specific to measurement tools focused on fine motor skills. First, the scope of hand function
assessed by a measurement tool should be considered. Measurement tools can focus on a single-concept task, a more complex task, or a series of tasks ranging in complexity. Next, upper extremity tremor is often asymmetrical (Farkas et al., 2006
; Louis, 2010
) and in some cases related to handedness
(Machowska-Majchrzak et al., 2011
; van der Hoorn et al., 2012
). A detailed evaluation of fine motor skills in tremor disorders requires selecting measurement tools that assess unilateral tasks in the dominant and non-dominant hands as well as bilateral tasks
(Héroux et al., 2006
). In other contexts, it may be more relevant to focus on a single task done with one hand. Finally, task familiarity can influence a performance and self-reported function. Performance of tasks usually improves with practice (Wulf et al., 2010
; Taylor and Ivry, 2012
) and individuals with tremor often develop compensatory strategies such as stabilizing their upper extremity on a firm surface to successfully accomplish them (Sanes et al., 1990
; Pascual-Leone et al., 1993
). These factors will impact tracking individuals over time or comparing between groups.