Table 3.

Item performance for each statistical criteria to select “best performing items” across traits

Shortlisted Items (items = 19)#	Traits	Scale - ESEM construct (loading score)	Expert rating (k*	Respondents endorsing scores >0 (%)	Correlation with log-PPTs (Spearman’s rho)
1. “I look forward with enjoyment to things”	Depression	HADS - Depression (0.93)	0.71	54%	-0.12*
2. “I still enjoy the things I used to enjoy”	Depression	HADS -Depression (0.82)	0.64	75%	-0.15*
3. “I can’t seem it keep it out of my mind”	Catastrophic thinking	PCS - Rumination (0.92)	0.71	52%	-0.11
4. “I keep thinking about how much it hurts”	Catastrophic thinking	PCS - Rumination (1.08)	0.83	59%	-0.13*
5. “I feel I can’t go on”	Catastrophic thinking	PCS - Helplessness (0.99)	0.78	24%	-0.09
6. “I feel I can’t stand it anymore”	Catastrophic thinking	PCS - Helplessness (0.93)	0.78	56%	-0.09
7. Is cold or heat (bath water) in this area occasionally painful?	Neuropathic Symptoms	MPDQ - Evoked symptoms (0.85)	0.73	43%	-0.23*
8. Over the past month, in your most painful knee, is light touching (clothing, a blanket) in this area painful?	Neuropathic Symptoms	MPDQ - Evoked symptoms (0.56)	0.79	40%	-0.21*
9. Over the past month, do you have a tingling or prickling sensation in the area of your most painful knee ‘pain’ (like crawling ants or electrical tingling)?	Neuropathic Symptoms	MPDQ - Spontaneous symptoms (1.15)	0.66	50%	-0.09
10. In the past week, how much has your knee pain that comes and goes affected your sleep?	Intermittent pain experience	Intermittent ICOAP - Somatic symptoms (0.71)	0.64	56%	-0.17*
11. In the past week, how upset or worried have you been by your knee pain that comes and goes?	Intermittent pain experience	Intermittent ICOAP - Psychological symptoms (0.76)	0.69	71%	-0.14*
12. In the past week, how frustrated or annoyed have you been by your constant knee pain?	Constant pain experience	Intermittent ICOAP - Psychological symptoms (0.78)	0.60	76%	-0.17*
13. In the past week, how upset or worried have you been by your constant knee pain?	Constant pain experience	Constant ICOAP - Psychological symptoms (0.90)	0.78	69%	-0.16*
14. In the past week, how much has your constant knee pain affected your sleep?	Constant pain experience	Constant ICOAP - Somatic symptoms (0.88)	0.78	68%	-0.21*
15. “I get a sort of frightened feeling as if something awful is about to happen”	Anxiety	HADS -Anxiety (0.83)	0.69	60%	-0.08
16. “I get sudden feelings of panic”	Anxiety	HADS -Anxiety (0.82)	0.61	53%	-0.19*
17. Knee pain plus other pain below the waist	Pain Distribution	-	0.81	52%	-0.14*
18. Does your pain or other bodily symptoms stop you from concentrating on what you are doing?	Cognitive Impact	-	0.71	74%	-0.18*
19. In the past month, did you feel tired on most days?	Fatigue	-	0.61	96%	-0.15*

Items in bold represent items selected as “best performing items”.

^*p<0.05 (Bonferroni corrected).

^#Items presented (items = 19) were rated by experts to show relevance to centrally augmented mechanisms following expert rating (k*>0.60).

Items originating from established scales showed the highest significant (p<0.05) associations with each identified latent construct during ESEM analysis. Domains measured by singular items (item specific domains) not entered into ESEM.

Hospital Anxiety and Depression scale (HADS); Modified PainDETECT Questionnaire (MPDQ); Pain Catastrophizing Scale (PCS), Intermittent and Constant Osteoarthritis Pain (ICOAP) scale.

Fatigue, Pain Distribution and Cognitive Impact measured by singular items.