Introduction This chapter will address three important and related dimensions of pain-related physical function. The first dimension, perceived interference, is typically measured using global ratings of the extent to which pain interferes with various key activities. Individuals make ratings in which they are typically asked to isolate the impact of pain from other aspects of their illness or lifestyle that interfere with daily activities. Not surprisingly, these ratings not only correlate with pain, but also with other psychological factors such as depression. The second dimension, activity level, is typically measured using ratings of what specific activities the individual participates in on a regular basis. These ratings are not tied to pain and do not take into account, in general, whether the activity is appropriate for the individual. And finally, the third dimension is sleep. Sleep is measured either with diaries or summary scales, and often ratings are made regarding the extent to which pain interferes with sleep. Challenges in selecting a scale There are a number of challenges that need to be considered before selecting a measure of pain-related physical function. First, most measures of pain-related physical function are correlated with ratings of pain intensity. Although correlated, the relationship has been shown to be non-linear, and a number of factor analyses that have combined measures of pain with measures of physical function often identify distinct factors. There is some indication from the literature reviewed below that ratings of interference made within specific domains – sleep, recreation, etc.
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