Evaluation of the psychometric properties of the Nighttime Symptoms of COPD Instrument

Figures & data

Table 1 Sociodemographic and clinical characteristics

Characteristics	Overall sample day 1a (n=1,663)
Age, mean (SD)	63.9 (8.9)
Sex female, n (%)	778 (46.8)
Race/ethnicity, n (%)
American Indian/Alaskan native	7 (0.4)
Asian	6 (0.4)
Black or African American	95 (5.7)
Native Hawaiian/Pacific Islander	2 (0.1)
White	1,550 (93.2)
Other	3 (0.2)
FEV1, mean (SD), L	1.4 (0.5)
FEV1, % predicted, mean (SD)^Citation1	49.0 (14.0)
FVC, mean (SD), L	2.77 (0.85)
SGRQ,b n	1,648
Total score, mean (SD)	46.5 (18.5)
Symptoms domain score, mean (SD)	65.1 (21.4)
Activity domain score, mean (SD)	60.6 (22.3)
Impacts domain score, mean (SD)	32.7 (19.4)
E-RS total,c mean (SD; n)	9.6 (6.30; 1,658)
GOLD stage, n (%)
I	4 (0.2)
II	946 (56.9)
III	696 (41.9)
IV	12 (0.7)

Notes:

a For patients who were missing the NiSCI diary entry on day 1 (day of randomization), data from the closest day before day 1 were used.

b SGRQ scores range from 0 to 100; higher score=more severe health status.

c The E-RS total score is an aggregate of three domains identified on the E-RS. Scores range from 0 to 40; higher score=more severe respiratory symptoms.

Abbreviations: SD, standard deviation; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; SGRQ, St George’s Respiratory Questionnaire; E-RS, Exacerbations of Chronic Obstructive Pulmonary Disease Tool-Respiratory Symptoms; GOLD, Global Initiative for Chronic Obstructive Lung Disease; NiSCI, Nighttime Symptoms of COPD Instrument.

Table 2 Patients’ experience of chronic obstructive lung disease symptoms at nighttime evaluated using the NiSCI: baseline weeka

NiSCI items	n	Mean (SD)	Median	Range
Cough severityb	1,630	0.77 (0.76)	0.57	0–3.8
Wheezing severityb	1,630	0.61 (0.74)	0.29	0–3.8
Shortness of breath severityb	1,630	0.76 (0.81)	0.50	0–3.8
Tightness in chest severityb	1,627	0.43 (0.65)	0	0–3.8
Chest congestion severityb	1,627	0.47 (0.70)	0	0–3.8
Difficulty with bringing up phlegm severityb	1,630	0.41 (0.76)	0	0–4.0
Overall nighttime symptoms severityb	1,630	1.03 (0.70)	1	0–3.8
Number of nighttime awakeningsc	243	2.03 (1.06)	1.8	1–≥10
Nighttime puffs of rescue medication	1,630	1.39 (1.49)	1	0–9.4

Notes:

a Baseline week: 7 days up to and including randomization day.

b 0=no symptoms; 1=mild; 2=moderate; 3=severe; and 4=very severe.

c Nighttime awakening is censored at ten times. Only those who answered “yes” to a question on if they woke up due to nighttime symptoms were included.

Abbreviations: NiSCI, Nighttime Symptoms of COPD Instrument; SD, standard deviation.

Table 3 Summary of NiSCI item analyses for decision making

n=831	Floor effect % (baseline day)	Floor effect % (baseline week)	Inter-item correlation (baseline day)	Inter-item correlation (baseline week)	CFA loading (baseline day)	CFA loading (baseline week)	IRT fit	Decision to reject or accept
NiSCI item 1a How many times did you wake up because of your COPD symptoms?	NA	NA	≤0.369	≤0.306	NA	NA	NA	Accept
NiSCI item 2ai How severe was your cough?	49.7%*	29.5%	≤0.269	≤0.727	0.690	0.758	Yes	Accept
NiSCI item 2bi How severe was your wheezing?	60.3%*	41.4%*	≤0.601	≤0.692	0.695	0.759	Yes	Accept
NiSCI item 2ci How severe was your shortness of breath?	54.2%*	32.1%*	≤0.719	≤0.801*	0.708	0.783	Yes	Accept
NiSCI item 2di How severe was the tightness in your chest?	72.0%*	51.0%*	≤0.559	≤0.634	0.729	0.775	Yes	Accept
NiSCI item 2ei How severe was your chest congestion?	69.2%*	51.4%*	≤0.541	≤0.625	0.781	0.839	Yes	Accept
NiSCI item 2fi How severe was the difficulty with bringing up phlegm?	79.1%*	61.3%*	≤0.519	≤0.622	0.674	0.692	Yes	Accept
NiSCI item 3 Overall, how severe were your COPD symptoms last night?	27.6%	13.0%	≤0.719	≤0.801	NA	NA	No	Accept but score separately
NiSCI item 7 How many puffs of your rescue medication did you take last night?	NA	NA	≤0.489	≤0.533	NA	NA	NA	Accept

Notes:

* Indicates values that are above the threshold criteria that were set a priori to flag items for potential problems (ie, floor effect minimum response >30% and ceiling effect maximum response >30%).

Abbreviations: NiSCI, Nighttime Symptoms of COPD Instrument; CFA, confirmatory factor analysis; IRT, item response theory; COPD, chronic obstructive pulmonary disease; NA, not applicable.

Figure 1 Final conceptual framework.

Abbreviation: COPD, chronic obstructive pulmonary disease.

Table 4 Correlationa of NiSCI scores with SGRQ, E-RS total, and FEV₁b at baseline week

	Six-item symptom severity scorec	Overall symptoms severity scored	Number of nighttime awakenings score	Rescue medication score
SGRQ total score	0.58***	0.57***	0.45***	0.35***
SGRQ symptoms score	0.66***	0.60***	0.45***	0.39***
SGRQ impacts score	0.55***	0.53***	0.45***	0.35***
E-RS total score	0.76***	0.73***	0.50***	0.36***
FEV1 (trough)b	−0.01	−0.04	0.01	−0.06

Notes:

a Spearman rank order correlation coefficients

*** P<0.0001.

b Morning predose value.

c Average score of six symptom severity items (cough, wheezing, shortness of breath, tightness in your chest, chest congestion, and difficulty bringing up phlegm).

d Single item on overall nighttime symptoms severity.

Abbreviations: NiSCI, Nighttime Symptoms of COPD Instrument; SGRQ, St George’s Respiratory Questionnaire; E-RS, Exacerbations of Chronic Obstructive Pulmonary Disease Tool-Respiratory Symptoms; FEV₁, forced expiratory volume in 1 second.

Figure 2 NiSCI scores by SGRQ total score at baseline week.

Notes: Values above bars indicate the mean (standard deviation) for each. Error bars represent standard error of the mean. Significance level for comparison: ***P<0.0001; sample median 47.48.

Abbreviations: NiSCI, Nighttime Symptoms of COPD Instrument; SGRQ, St George’s Respiratory Questionnaire; SE, standard error.

Figure 3 NiSCI scores by SGRQ symptom score at baseline week.

Notes: Values above bars indicate the mean (standard deviation) for each. Error bars represent standard error of the mean. Significance level for comparison: ***P<0.0001; sample median 69.46.

Abbreviations: NiSCI, Nighttime Symptoms of COPD Instrument; SGRQ, St George’s Respiratory Questionnaire; SE, standard error.

Figure 4 NiSCI scores by E-RS score at baseline week.

Notes: Values above bars indicate the mean (standard deviation) for each. Error bars represent standard error of the mean. Significance level for comparison: **P<0.001; ***P<0.0001; sample median 11.

Abbreviations: NiSCI, Nighttime Symptoms of COPD Instrument; E-RS, Exacerbations of Chronic Obstructive Pulmonary Disease Tool-Respiratory Symptoms; SE, standard error.

Figure 5 NiSCI scores by GOLD severity stages II and III at baseline week.

Notes: Values above bars indicate the mean (standard deviation) for each. Error bars represent standard error of the mean. Significance level for comparison: **P<0.001;***P<0.0001.
Abbreviations: NiSCI, Nighttime Symptoms of COPD Instrument; GOLD, Global Initiative for Chronic Obstructive Lung Disease; SE, standard error.

BhullarSPhillipsBSleep in COPD patientsCOPD20052335536117147000

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