TABLE 7.

Clustering of keywords in COPD drugs-related studies that were published from 1980 to 2021.

Cluster	Size	Silhouette	Mean (Year)	Label (LLR)
0	203	0.564	2002	COPD
1	94	0.824	1997	Exercise
2	85	0.902	2000	Emphysema
3	76	0.901	1998	Metabolism
4	71	0.921	1996	Hypoxia
5	62	0.939	1998	Recurrent airway obstruction
6	58	0.861	1996	Oxitropium bromide
7	58	0.879	2000	Airway resistance
8	58	0.938	1997	Disease
9	56	0.896	2000	Antibiotic therapy
10	55	0.866	2000	Theophylline
11	54	0.937	1998	Respiratory muscles
12	46	0.939	1999	Expression
13	43	0.934	1996	Pharmacokinetics
14	33	0.907	2000	Trial
15	31	0.962	2000	Heart failure
16	20	0.958	1997	Elderly
17	16	0.999	1999	Candidate gene
18	14	0.986	2000	Ipratropium
19	10	0.999	2002	Pulmonary drug delivery
21	10	0.992	2001	Alveolar development
22	9	0.998	2003	COPD
23	8	0.996	1998	Xylazine
26	7	1	1991	Screening test
30	4	0.995	2004	Logistic models
35	3	1	2000	Industrial area