Page 80 - THE PERCEPT STUDY Illness Perceptions in Physiotherapy Edwin de Raaij

Chapter 4
Pain duration
Participants were asked how long their pain had existed prior to consultation. We categorized the outcomes into 3 groups:
• acute pain < 7 weeks
• subacute pain 7 – 13 weeks
• persistent pain > 13 weeks
Psychological measures
The Four-Dimensional Symptom Questionnaire (4DSQ) was used to assess participants’ levels of risk for distress, depression, anxiety, and somatization: it is reported to show good reliability . Sum scores were calculated and cut-off points28 applied to categorize each participant as being at low, medium or high risk .(Box 2)
Illness perceptions
The Brief IPQ-DLV was used as it has acceptable psychometric properties8,13. This questionnaire consists of nine questions: eight questions are scored on a 0 – 10 scale; the ninth question is an open-ended question about the dimension ‘Cause’.
Statistics
Descriptive statistics of demographic variables were reported as mean and standard deviation. Missing value analysis was performed and < 5% missing data was assumed to be inconsequential24. For sample size in stepwise regression, several rules of thumbs are reported in literature. Ranging from 50 participants + 8 - 30 per independent variable. We used a rule of thumb for a minimum sample size of 50 + >30 per independent variable based on the recommendations when expecting small associations30. The one-way ANOVA with Tukey post-hoc test was used to examine the differences between the three pain duration groups.
To examine the additional association of illness perceptions with pain intensity or limitation in physical functioning, a multiple linear regression was used. First, age, gender and the well-known prognostic factors were entered as ‘fixed’ in the model. Second, with univariate
Box 2: cut off points 4DSQ
Low risk Medium risk High risk
Distress Depression Anxiety 0-10 0-2 0-3 11-20 3-5 4-9 21-32 6-12 10-24
Somatization 0-10
11-20 21-32
78