Sample
See Table
1 for the participant characteristics. There were no significant differences between the Dutch CFS, UK CFS, and healthy control cohorts in terms of gender (χ
2 (2) = 4.56,
p = .10), employment (χ
2 (2) = .21,
p = .90), type of employment (full or part-time), (χ
2 (2) = .74,
p = .69), or marital status (χ
2 (6) = 11.16,
p = .69,
p = .08). There was a significant difference between the groups in education attainment (χ
2 (2) = 24.10,
p ≤ .001); with more of the Dutch CFS participants in the low education category
3 than either the UK CFS or UK healthy control groups (both
p < .05). Sensitivity analysis of subsequent analyses found no difference in effects when controlling for level of education. Healthy participants were significantly younger than either UK CFS participants,
U = 1025,
p = .05, or Dutch CFS participants,
t(63.83) = 2.09,
p = .04. Age was not correlated with any of the main outcomes so was not controlled for in subsequent analyses. As expected, UK and Dutch CFS groups had significantly higher rates of anxiety, depression, and disability compared to healthy participants (all
p < .05).
Table 1
Demographic variables and scores on self-report measures and information processing tasks for the Dutch and UK CFS patients and UK healthy controls
Age (years M, SD) | 40 (13) | 39 (12) | 34 (10) |
Female, n (%) | 16 (42) | 32 (62) | 32 (63) |
Employed, n (%) | 24 (65) | 36 (69) | 35 (69) |
Full-time, n (%) | 13 (34) | 20 (38) | 22 (43) |
Education level: low | 27 (71%) | 15 (29%) | 13 (26%) |
Marital status |
Single | 13 (34%) | 23 (44%) | 29 (57%) |
Married/living together | 24 (63%) | 25 (48%) | 20 (39%) |
Divorced | 0 | 4 (.08%) | 1 (.02%) |
Widowed | 1(.03%) | 0 | 1 (.02%) |
CFQ, M (SD) | 24.97 (4.05) | 26.83 (4.71) | 10.7 (3.3) |
WSAS, M (SD) | 23.6 (7.29) | 23.38 (8.81) | 0.5 (2.2) |
HADS anxiety, M (SD) | 6.41 (3.86) | 9.96 (4.84) | 4.69 (3.43) |
HADS depression, M (SD) | 9.0 (4.28) | 8.44 (4.0) | 2.04 (2.38) |
Visual-probe task, M (SD)1
|
Attentional bias score | .28 (1.16) | .22 (.90) | − .20 (.82) |
Interpretation bias task, M (SD) |
Somatic interpretations | 2.28 (.51) | 2.24 (.59) | 2.02 (.41) |
Positive interpretations | 2.69 (.39) | 2.74 (.49) | 3.05 (.42) |
Attentional control task, M (SD) |
RT to congruent trials | 652.95 (222.05) | 588.86 (136.58) | 510.25 (80.34) |
RT to incongruent trials | 793.20 (236.38) | 722.85 (172.48) | 615.94 (95.81) |
Attentional control score | 140.25 (104.02) | 133.62 (73.58) | 105.70 (50.4) |
The Dutch and UK CFS groups had equivalent levels of fatigue (CFQ),
t(88) = − 1.94,
p = .06; functioning (WSAS),
t(88) = .03,
p = .90; and depression,
t(88) = .63,
p = .53. The Dutch CFS group had significantly lower levels of anxiety compared to the UK CFS group,
t(88) = − 3.71,
p < .001.
4
VPT: Attentional Bias in UK and Dutch CFS Groups and Healthy Controls
A one-way ANOVA with AB scores showed a significant main effect of group, F(2, 136) = 3.46; p = .03; ηp
2 = .05. Compared to healthy controls, the Dutch CFS group had a significant AB towards illness-related stimuli, F(1, 84) = 4.98; p = .03; ηp
2 = .06. There were no differences in AB scores between Dutch and UK CFS groups, F(1, 86) = .07; p = .80; ηp
2 = .001.
The main effect remained when controlling for anxiety, F(3, 136) = 3.25 p = .04; ηp
2 = .05, but disappeared when controlling for depression, F(3, 136) = 1.17; p = .31; ηp
2 = .02.
Recognition Task: Interpretation Bias in UK and Dutch CFS Groups and Healthy Controls
There was a significant group x valence interaction F(2, 138) = 16.84, p < .001, ηp
2 = .20, which remained significant when controlling for anxiety, F(3, 136) = 12.60, p < .001, ηp
2 = .16; and depression F(3, 136) = 10.44, p < .001, ηp
2 = .13.
The Dutch CFS group endorsed positive interpretations significantly less than healthy controls, t(87) = − 4.17, p < .001, 95% CI (− 54, − .19); and somatic interpretations significantly more than healthy controls, t(87) = 2.61, p = .01, 95% CI (.06, 45). There was no significant differences between the CFS groups in ratings of somatic, t(88) = .36, p = .72, 95% CI (− .19, .28) or positive interpretations, t(88) = − .71, p = .48, 95% CI (− .23, .11).
ANT: Attentional Control in UK and Dutch CFS Groups and Healthy Controls
There was a non-significant trend towards a main effect of group on attentional control scores, F(2, 138) = 2.72, p = .069, ηp
2 = .04. Separate ANOVAs indicated the Dutch CFS group had significantly poorer attentional control than healthy participants, F(1, 87) = 4.29, p = .04, ηp
2 = .05; but equivalent attentional control to the UK CFS group, F(1, 88) = .126, p = .72, ηp
2 = .001.
Moderating Role of Attentional Control on Attention and Interpretation Biases
A linear regression with AB scores as the criterion and the interaction term and group as predictor variables, found attentional control did not moderate the relationship between group and AB; b ≤ .02, SEb = .001, β = .31, t(136) = .1.58, p = .12, 95% CI (− .00,.004). A separate linear regression with IB index as the criterion found attentional control was not a significant moderator of the relationship between group and IB; b = − 3.85, SEb = .001, β = − .01, t(140) = − .05, p = .96, 95% CI (− .002, .001).