Sick and Tired: Understanding and Managing Sleep Difficulties in ...

diagnostic criteria for these sleep disorders (such as periodic limb movement disorder,
bruxism, sleep apnea or restless legs syndrome).
The findings of this thesis should be interpreted with some caution as the analyses did
not account for possible measurement and sampling error. As little research has been
completed in the field of FMS using the measures incorporated within this thesis, little
is known about the psychometric properties of these measurement tools with the FMS
population. Consideration of the most evidence based measures for use within this
thesis (as described in Chapter Four) and procedures for reducing systematic error were
applied (such as double entering data, the measures being administered by one trained
researcher). However, despite these efforts there remains a risk of measurement error;
(that the assessment tools do not measure what they state they are measuring or due to
human consistency) which may bias the results. There may be a particular risk of
possible misclassification of participants into outcome groups for the logistic regression,
(as conducted in Chapter 5) due to measurement error and therefore caution needs to be
applied in the interpretation of these findings.
There is a need for further studies to explore the psychometric properties of these
assessment tools in more detail to ensure the accuracy of research findings. It has been
found that measurement error can reduce the power of a study by over 25% (Cheng,
Branscum, & Stamey, 2010). Therefore, in future studies it is recommended that
adjustments for possible sampling error be made in sample size calculations for studies
utilising these tools, particularly when exploring constructs that are known to frequently
occur within a given population. As the high frequency of sleep difficulties was
unknown at the time of study completion, this was not accounted for within this thesis;
but on reflection accounting for this risk of error would have increased confidence in the
research findings.
Participants were recruited through community based support groups and although this
approach was chosen to ensure the capture of people with varying degrees of severity of
FMS (rather than only those requiring support from hospital services or specialist
clinics), this may limit the generalisability of the results to people who do not attend
support groups. People attending support groups may differ from people with FMS who
do not, such as an increased need for social support or seeking information (Davison,
Pennebaker, & Dickerson, 2000). For example, it was found in a study in HIV patients
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