Is the St. George’s Respiratory Questionnaire an Appropriate Measure of Symptom Severity and Activity Limitations for Clinical Trials in COPD? Analysis of Pooled Data from Five Randomized Clinical Trials

Figures & data

Figure 1 Conceptualization of the SGRQ “Symptoms” domain.

Table 1 Summary of the Demographics of the Samples from the Five Clinical Trials Used for the Rasch Measurement Theory Analysis of the SGRQ in Chronic Obstructive Pulmonary Disease

	Study
	Shine (A2303) N=2135	Spark (A2304) N=2207	Lantern (A2331) N=741	Flight-1 (A2336) N=1038	Flight-2 (A2337) N=998	Total N=7119
Age – Mean (SD)	63.92 (8.83)	63.29 (7.99)	65.03 (7.87)	63.81 (8.31)	63.06 (8.39)	63.70 (8.35)
Male - n(%)	1610 (75.4%)	1650 (74.8%)	672 (90.7%)	705 (67.9%)	584 (58.5%)	5221 (73.3%)
COPD severity (GOLD) - n(%)
Mild (GOLD 1)	2 (0.1%)	0 (0.0%)	3 (0.4%)	0 (0.0%)	0 (0.0%)	5 (0.1%)
Moderate (GOLD 2)	1358 (63.6%)	2 (0.1%)	387 (52.2%)	632 (60.9%)	605 (60.6%)	2984 (41.9%)
Severe (GOLD 3)	775 (36.3%)	1747 (79.2%)	344 (46.4%)	400 (38.5%)	384 (38.5%)	3650 (51.3%)
Very severe (GOLD 4)	0 (0.0%)	458 (20.8%)	0 (0.0%)	1 (0.1%)	0 (0.0%)	459 (6.4%)
Baseline FEV1 Post-Bronchodilator (% pred. FEV1) – Mean (SD)	51.94 (12.77)	35.16 (7.74)	47.74 (11.76)	54.61 (13.48)	54.57 (13.06)	47.03 (14.13)
Smoking history of subject - n(%)
Ex-smoker	1288 (60.3%)	1378 (62.4%)	549 (74.1%)	526 (50.7%)	461 (46.2%)	4202 (59.0%)
Current smoker	847 (39.7%)	829 (37.6%)	192 (25.9%)	512 (49.3%)	537 (53.8%)	2917 (41.0%)
Baseline SGRQ Symptoms score – Mean (SD)	58.44 (20.97)	60.08 (21.29)	45.46 (19.79)	60.65 (21.93)	60.66 (21.04)	58.23 (21.56)
Baseline SGRQ Activity score – Mean (SD)	61.82 (20.54)	69.31 (19.27)	53.08 (17.48)	64.63 (18.54)	65.95 (18.85)	64.22 (19.91)
Baseline SGRQ Impact score – Mean (SD)	35.02 (20.92)	40.48 (20.52)	29.04 (17.55)	36.12 (18.92)	37.12 (19.93)	36.54 (20.32)

Abbreviations: COPD, chronic obstructive pulmonary disease; GOLD, global initiative for chronic obstructive lung disease; SD, standard deviation; SGRQ, St. George’s Respiratory Questionnaire.

Table 2 SGRQ “Activity” Domain: Item Fit to the Rasch Model with and without Items 11 and 17 and Differential Item Functioning (DIF) by Geographical Region (Baseline Visits, Pooled Data from 5 Trials, N=7,116)

	Full SGRQ Activity Item Set		SGRQ Activity Item Set without Items 11 and 17
Item	Fit Residual	χ^2	Fit Residual^Citation1	χ^2	DIF by Geographical Region
11. Sitting or lying still makes feel breathless	8.74	337.7
12. Getting washed or dressed makes feel breathless	−5.94	259.0	−2.40	196.9	Non-uniform
13. Walking around the home makes feel breathless	−1.40	144.1	0.79	109.5	Non-uniform
14. Walking outside on the level makes feel breathless	−1.83	167.6	1.28	158.1	Uniform
15. Walking up a flight of stairs makes feel breathless	−3.10	65.0	−2.29	52.1	Non-uniform
16. Walking up hills makes feel breathless	1.54	64.0	3.64	119.9	Non-uniform
17. Playing sports or games makes feel breathless	4.80	245.5
36. Long time to get washed/get dressed	−5.45	250.9	−3.86	231.2	Non-uniform
37. Cannot or take a long time to take bath or shower	−1.19	96.3	−0.33	59.6	Non-uniform
38. Walk slower than other people, or must stop for rest	−4.04	186.9	−3.54	172.5	Uniform
39. Housework takes a long time	−6.86	266.4	−5.82	226.5	Non-uniform
40. Must stop or slow down walking up one flight of stairs	−4.25	218.8	−4.22	218.2	Non-uniform
41. Must stop or slow down hurrying or walking fast	−5.75	125.0	−5.99	106.9	Non-uniform
42. Breathing makes mild activity (eg walk up hill) difficult	−4.74	90.4	−4.22	80.6	Non-uniform
43. Breathing makes moderate activity (eg jog) difficult	−3.66	44.8	−3.62	37.1	Non-uniform
44. Breathing makes intense activity (eg run or cycle) difficult	−0.48	36.2	0.52	39.2	Uniform

Notes: In bold, fit residuals outside the range of −2.5/2.5; χ² values with p-values<0.001. Adapted with permission from St George’s University of London. Available from: http://www.healthstatus.sgul.ac.uk/SGRQ_download/SGRQ%20Manual%20June%202009.pdf. Accessed September 02, 2020.²⁷

Abbreviations: SGRQ, St. George’s Respiratory Questionnaire; DIF, differential item functioning.

Figure 2 Person-item distribution of the SGRQ “Activity” domain without items 11 and 17 (Baseline visits, pooled data from 5 trials, N=7,116). The top part of the figure (purple) shows the distribution of impact on activity level in the sample, and the lower part (blue) shows the distribution of impact on activity level in the SGRQ “Activity” domain item thresholds. The blue diamonds corresponds to the “thresholds” between two adjacent item response categories (presented in Figure 4).

Figure 3 Comparison of SGRQ Activity item location estimates obtained from each trial separately vs obtained from pooled five trials.

Figure 4 RMT analysis of the SGRQ “Activity” domain without item 11: item hierarchy (Baseline visits from 5 trials, N=7,116).

Table 3 SGRQ “Symptoms” Domain: Item Fit to the Rasch Model Before and After Recoding Response Options (Baseline Visits, Pooled Data from 5 Trials, N=7,116)

	SGRQ Symptoms Item Set		SGRQ Symptoms Item Set With Recoded Response Options
Item	Fit Residual	Chi^2	Fit Residual	Chi^2
1. Coughed	−4.00	181.5	−6.44	160.5
2. Brought up phlegm (sputum)	2.71	100.1	−0.69	75.3
3. Shortness of breath	−5.68	205.4	−6.40	155.7
4. Attacks of wheezing	−2.38	212.6	−5.41	185.0
5. Number of severe attacks	−2.55	236.1	−0.68	249.9
6. Duration of worst attack	8.13	294.6	9.01	238.1
7. Number of good days	4.01	52.5	3.44	16.4
8. Worse in the morning	11.30	22.3	12.47	27.8

Notes: In bold, fit residuals outside the range of −2.5/2.5; χ² values with p-values<0.001. Adapted with permission from St George’s University of London. Available from: http://www.healthstatus.sgul.ac.uk/SGRQ_download/SGRQ%20Manual%20June%202009.pdf. Accessed September 02, 2020.²⁷

Abbreviation: SGRQ, St. George’s Respiratory Questionnaire.

Figure 5 Person-threshold distribution of the SGRQ “Symptoms” domain after item recoding (Baseline visits from 5 trials, N=7,116). The top part of the figure (purple) shows the distribution of symptoms level in the sample, and the lower part (blue) shows the distribution of symptoms level in the SGRQ ‘Symptoms’ domain item thresholds. The blue diamonds corresponds to the “thresholds” between two adjacent item response categories (presented in Figure 6).

Figure 6 Thresholds map of the SGRQ “Symptoms” domain after item recoding (Baseline visits from 5 trials, N=7,116).

MiravitllesM, RiberaA. Understanding the impact of symptoms on the burden of COPD. Respir Res. 2017;18(1):67. doi:10.1186/s12931-017-0548-328431503

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St George’s University of London. Available from: http://www.healthstatus.sgul.ac.uk/SGRQ_download/SGRQ%20Manual%20June%202009.pdf. Accessed September 02,2020

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