Relationships in longitudinal design

4.4.5.1 The Outcomes at one month post-operative

There were two sets of pre-operative psychological factors. First, all significant correlations of psychological factors at baseline with post-operative outcomes at one month are displayed in Table 18. All outcomes were significantly correlated with fear except hip symptoms. Hip pain, function, and overall QOL were significantly related to both fears.

Hip-related QOL and SRH were reported the significant relationship with only fear of anaesthesia. The worse fear of anaesthesia at baseline was reported in the patients that tended to have worse pain, functions, and QOL at one month post-operative. All correlations are shown in Appendix 24.

Second, two significant relationships between the outcomes at one month post-operative and two factors at one-month pre-operative were reported: hip related QOL with self-efficacy of symptoms (rs = -0.55, p = 0.042); and hip symptoms with pain expectation at one year post-operative (rs = -0.68, p = 0.010). A correlation matrix (N=14) is displayed in Appendix 25. Moreover, the adjusted p-value was calculated as 0.0001 from 484 correlational tests. Two values of the significant results were more than the adjusted p-value and should be viewed in isolation with caution.

Table 18: Summary of significant correlations of the post-operative one-month outcomes with pre-operative predictors at baseline (N=25)

Outcomes Psychological factors correlated in (rs, p-value)

Large effect size (rs > 0.50) Moderate effect size ( 0.30 < rs ≤ 0.50)

Subsequently, simple linear regression was performed. The predictor was fear of anaesthesia included in the analysis with two outcomes: hip pain; and hip-related QOL.

The standardised regression coefficients (beta), R², adjusted R² and p-value of each linear model are displayed in Table 19.

Table 19: Simple linear regression of fear of anaesthesia measuring at baseline with the post-operative outcomes at one month

Hip pain (N=25) Hip-related QOL (N=25)

Beta -0.446 -0.442

R² 0.199 0.196

Adjusted R² (p-value) 0.164 (p = 0.025) 0.181 (p = 0.027)

A model of hip pain was created with fear of anaesthesia. Significant difference from zero of the regression coefficient ((F(1, 23) = 5.719, p = 0.025), with R² = 0.199), showed that around 20% of the variance in hip pain was predicted by fear of anaesthesia. Patients, who had pre-operative worse fear of anaesthesia, were more likely to report post-operatively

high pain at the hip. The other linear regression of hip-related QOL with fear of anaesthesia was performed and showed significant difference from zero of regression coefficient ((F(1, 23) = 5.600, p= 0.027), with R² = 0.196). This indicated that around 20% of the variance in hip-related QOL was predicted by fear of anaesthesia. Patients who had worse fear of anaesthesia before THR were more likely to report worse post-operative hip-related QOL at one month. Pre-operative fear of anaesthesia at baseline predicted post-operative one-month hip pain and hip-related QOL.

4.4.5.2 The Outcomes at six months post-operative

Significant correlations in large effect size of post-operative outcomes at six months with pre-operative predictors at baseline are displayed in Table 20. The top three ranking of the high coefficients were pain catastrophising, self-efficacy of symptoms, depression, and pre-operative two-week expectation of pain. Full details of correlations are shown in Appendix 26. However, correlations of outcomes at six months post-operative with predictors at one month pre-operative were unable to analyse.

Table 20: Summary of significant correlations in large effect size of the post-operative six-month outcomes with pre-operative predictors at baseline (N=14)

Outcomes Psychological factors correlated in large effect size (rs > 0.50) (r, p-value) Hip symptoms  Depression (rs = -0.55, p = 0.035)

 Pain catastrophising (rs = -0.65, p = 0.009)*

 Self-efficacy of symptoms (rs = 0.60, p = 0.025)*

 Pre-operative two-week expectation of pain (rs = -0.56, p = 0.032)*

 Post-operative six-month expectation of pain (rs = -0.55, p = 0.036) Hip pain  Depression (rs = -0.57, p = 0.027)

 Pain catastrophising (rs = -0.67, p = 0.006)*

 Self-efficacy of symptoms (rs = 0.62, p = 0.017)*

 Pre-operative two-week expectation of pain (rs = -0.63, p = 0.012)*

Hip function (ADL)

 Positive affect (rs = 0.53, p = 0.041)*

 Pain catastrophising (rs = -0.56, p = 0.029)*

 Self-efficacy of symptoms (rs = 0.63, p = 0.017)*

Hip function (sports)

 Depression (rs = -0.65, p = 0.023)*

 Fear of anaesthesia (rs = -0.59, p = 0.042)*

Outcomes Psychological factors correlated in large effect size (rs > 0.50) (r, p-value)

 Pre-operative two-week expectation of function (rs = -0.59, p = 0.034) Overall QOL  Depression (rs = -0.63, p = 0.009)*

 Pre-operative two-week expectation of function (rs = -0.58, p = 0.038) SRH  Depression (rs = -0.84, p<0.001)*

 Pre-operative two-week expectation of function (rs = -0.66, p = 0.013)

*Three highest values of correlation coefficients in each outcome.

The Bonferroni correction was calculated. The number of tests was 576, and the adjusted p-value was then calculated as 0.00008. Correlations remained significant for three of the factors with p-values of less than the adjusted p-value. They consisted of the correlations of hip-related QOL and overall QOL with pain catastrophising, and SRH with depression.

Other correlations highlighted above should be viewed in isolation with caution owing to the risk of familywise error.

All significant psychological factors are represented in Table 21 and Table 22. First, cross-sectional relationships and predictors were summarised from correlational and multiple regression analysis. The relationships between self-efficacy and the outcomes were found in all points of time whereas expectations were reported the correlations with the outcomes prior to initial assessment and six months post-operative. Depression was significantly related to the THR outcomes in pre-operative period. At one month

post-operative, emotional aspect was raised their relationships with the outcomes in particular anxiety, negative moods, and fear of anaesthesia. Finally, pain catastrophising was highly related to the outcomes at pre-operative period and six months post-operative.

Table 21: Summary of highly correlated psychological factors with the outcomes in cross-sectional analysis

The longitudinal relationships were concluded from correlational and simple linear regression. The outcomes at one month post-operative were highly related to fear at baseline and self-efficacy and expectation at two weeks pre-operative. The outcomes at six months post-operative were significantly related to depression, pain catastrophising, self-efficacy of symptoms, and pain expectation at two weeks pre-operative.

Table 22: Summary of highly correlated psychological factors with the outcomes in longitudinal analysis

At one month post-operative At six months post-operative Factors at baseline

 Fear of anaesthesia*

 Fear of THR

Factors at one month pre-operative

 Self-efficacy of symptoms

 Post-operative one-year expectation of pain

Factors at baseline

 Depression

 Pain catastrophising

 Self-efficacy of symptoms

 Pre-operative one-month expectation of pain

*regression analysis

4.5 Discussion