General lung function characteristics of the population
| Total population, n = 1559 | Without COPD, n = 1259 | With COPD, n = 340 | p-value | |
|---|---|---|---|---|
| Weight, kg, n (SD) | 70.6 (13.74) | 71.4 (13.86) | 67.7 (12.86) | <0.001 |
| Height, cm, n (SD) | 159.6 (9.25) | 159.6 (9.29) | 159.7 (9.10) | 0.954 |
| Pulmonary function, L (SD) | ||||
| FVC reference | 3.1 (0.81) | 3.1 (0.82) | 3.0 (0.8) | 0.014 |
| FVC pre-B2 | 2.9 (0.98) | 3.0 (0.99) | 2.7 (0.92) | <0.001 |
| FVC pre-B2, % predicted | 94.7 (21.33) | 96.3 (20.76) | 88.8 (22.36) | <0.001 |
| FVC post-B2 | 3.0 (0.97) | 3.1 (0.97) | 2.9 (0.97) | 0.001 |
| FVC post-B2, % predicted | 98.1 (21.02) | 98.7 (20.48) | 95.8 (22.77) | 0.031 |
| FVC, % change | 4.2 (7.97) | 2.9 (6.75) | 9.1 (9.98) | 0.001 |
| FEV1 reference | 2.4 (0.67) | 2.5 (0.67) | 2.3 (0.64) | <0.001 |
| FEV1 pre-B2, best | 2.2 (0.82) | 2.4 (0.77) | 1.5 (0.61) | <0.001 |
| FEV1 pre-B2, % predicted | 90.6 (25.02) | 97.0 (21.69) | 66.6 (21.81) | <0.001 |
| FEV1 post-B2, best | 2.3 (0.82) | 2.5 (0.78) | 1.7 (0.64) | <0.001 |
| FEV1 post-B2, % predicted | 96.4 (9.96) | 102.2 (21.31) | 74.9 (22.40) | <0.001 |
| FEV1, % change | 7.9 (9.96) | 6.0 (7.26) | 14.9 (14.5) | <0.001 |
| FEV/FVC reference | 78.2 (4.78) | 78.9 (3.16) | 75.7 (7.90) | <0.001 |
| FEV/FVC pre-B2%, best | 74.6 (12.79) | 79.4 (7.83) | 56.7 (11.73) | <0.001 |
| FEV/FVC pre-B2, % predicted | 94.9 (11.45) | 100.7 (9.17) | 73.7 (73.66) | <0.001 |
| FEV/FVC post-B2%, best | 76.8 (12.4) | 81.7 (6.86) | 58.6 (11.32) | <0.001 |
| FEV/FVC post-B2, % predicted | 98.0 (15.41) | 103.7 (9.01) | 76.5 (15.37) | <0.001 |
Validity analysis of the LFQ questionnaire with diagnosis of COPD
| S | 95% CI | E | 95% CI | VPP | 95% CI | VPN | 95% CI | LR+ | 95% CI | LR– | 95% CI | Index of accuracy | Youden's index | NND | NNMD | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Total population | 91.18 | 88.0–94.3 | 32.41 | 29.8–35.0 | 26.70 | 24.1–29.3 | 93.15 | 90.7–95.6 | 1.34 | 1.28–1.42 | 0.27 | 0.19–0.39 | 0.44 | 0.23 | 4 | 2 |
| Without symptoms | 80.77 | 63.7–97.8 | 62.91 | 56.2–69.6 | 21.00 | 12.5–29.5 | 96.40 | 92.9–99.9 | 2.17 | 1.69–2.81 | 0.3 | 0.14–0.68 | 0.64 | 0.43 | 2 | 3 |
| With symptoms | 92.04 | 88.9–95.2 | 26.20 | 23.5–28.9 | 27.24 | 24.5–29.9 | 91.64 | 88.3–94.9 | 1.24 | 1.19–1.31 | 0.3 | 0.21–0.45 | 0.41 | 0.18 | 5 | 2 |
| No smoking | 85.00 | 79.2–90.9 | 43.20 | 39.5–46.9 | 25.33 | 21.6–29.1 | 92.71 | 89.7–95.7 | 1.49 | 1.37–1.64 | 0.34 | 0.24–0.51 | 0.5 | 0.28 | 4 | 2 |
| Smoking | 96.67 | 93.7–99.6 | 18.63 | 15.3–21.9 | 27.88 | 24.3–31.5 | 94.50 | 89.8–99.2 | 1.18 | 1.13–1.25 | 0.17 | 0.08–0.40 | 0.37 | 0.15 | 7 | 2 |
| No exposure to wood smoke | 87.62 | 80.8–94.4 | 36.62 | 32.5–40.7 | 20.67 | 16.8–24.6 | 94.01 | 90.6–97.4 | 1.38 | 1.26–1.52 | 0.33 | 0.20–0.57 | 0.44 | 0.24 | 4 | 2 |
| Exposure to wood smoke | 92.77 | 89.2–96.3 | 29.06 | 25.6–32.5 | 30.45 | 27.0–33.9 | 92.31 | 88.6–96.1 | 1.3 | 1.23–1.39 | 0.24 | 0.16–0.40 | 0.45 | 0.21 | 5 | 2 |
| Without smoker in the home | 91.35 | 87.8–94.9 | 34.62 | 31.5–37.8 | 29.00 | 25.9–32.1 | 93.20 | 90.4–96.0 | 1.39 | 1.32–1.48 | 0.24 | 0.17–0.37 | 0.47 | 0.25 | 4 | 2 |
| With smoker in the home | 90.00 | 81.6–98.4 | 28.64 | 22.2–36.0 | 26.87 | 20.5–33.2 | 90.77 | 82.9–98.6 | 1.26 | 1.12–1.42 | 0.34 | 0.16–0.77 | 0.42 | 0.18 | 5 | 2 |
| Without smoking and without exposure to wood smoke | 76.19 | 62.1–90.3 | 47.74 | 41.8–53.7 | 17.58 | 11.8–23.4 | 93.20 | 88.8–97.6 | 1.45 | 1.19–1.78 | 0.49 | 0.29–0.87 | 0.92 | 0.23 | 4 | 14 |
| With smoking and exposure to wood smoke | 97.44 | 94.1 – 100 | 12.72 | 8.7–16.8 | 31.58 | 26.7–36.5 | 92.31 | 82.7–100 | 1.11 | 1.06–1.18 | 0.2 | 0.06–0.64 | 0.37 | 0.1 | 10 | 2 |
| Without symptoms | 80.77 | 63.7–97.8 | 62.91 | 56.2–69.6 | 21.00 | 12.5–29.5 | 96.40 | 92.9–99.9 | 2.17 | 1.69–2.81 | 0.3 | 0.14–0.68 | 0.64 | 0.43 | 2 | 3 |
| No exposure to wood smoke | 87.62 | 80.8–94.4 | 36.62 | 32.5–40.7 | 20.67 | 16.8–24.6 | 94.01 | 90.6–97.4 | 1.38 | 1.26–1.52 | 0.33 | 0.20–0.57 | 0.44 | 0.24 | 4 | 2 |
Results of the correlation analysis and concordance using LFQ questionnaire
| Correlation coefficient | 95% CI | p-value | |
|---|---|---|---|
| t-tests for related samples | 0.793 | ||
| Pearson's correlation coefficient | 0.884 | <0.001 | |
| Spearman's correlation coefficient | 0.881 | <0.001 | |
| ICC | 0.884 | 0.863–0.901 | <0.001 |
| Cronbach's alpha | 0.938 | ||
| Kappa correlation coefficient | 0.797 | <0.001 | |
| ICC FEV1 pre, L, vs LFQ | 0.165 | 0.117–0.212 | <0.001 |
| ICC FEV1 post, L, vs LFQ | 0.158 | 0.110–0.206 | <0.001 |
| ICC FEV1/FVC pre, L, vs LFQ | 0.179 | 0.131–0.226 | <0.001 |
| ICC FEV1/FVC post, L, vs LFQ | 0.183 | 0.135–0.230 | <0.001 |
Results of the LFQ questionnaire in the general population and in patients with and without COPD
| Total population, n = 1599 | Without COPD, n = 1259 | With COPD, n = 340 | p-value | |
|---|---|---|---|---|
| How often do you have a cough with mucus? | ||||
| Never, n (SD) | 348 (21.76) | 298 (23.6) | 50 (14.7) | <0.001 |
| Rarely, n (SD) | 591 (36.96) | 481 (38.2) | 110 (32.3) | |
| Sometimes, n (SD) | 351 (21.95) | 274 (21.7) | 77 (22.64) | |
| Frequently, n (SD) | 208 (13) | 141 (11.1) | 67 (19.7) | |
| Very often, n (SD) | 101 (6.3) | 65 (5.16) | 36 (10.58) | |
| How often do you fee sounds in your chest (gasps, whistles or vibrations) when you breathe? | ||||
| Never, n (SD) | 664 (41.5) | 583 (46.3) | 81 (23.82) | <0.001 |
| Rarely, n (SD) | 310 (19.38) | 253 (20.1) | 57 (16.76) | |
| Sometimes, n (SD) | 366 (22.88) | 260 (20.6) | 106 (31.1) | |
| Frequently, n (SD) | 169 (10.56) | 111 (8.81) | 58 (17.05) | |
| Very often, n (SD) | 90 (5.62) | 52 (4.13) | 38 (11.17) | |
| How often are you short of breath during a physical activity (when climbing stairs or climbing a slope without resting)? | ||||
| Never, n (SD) | 324 (21.6) | 272 (21.6) | 52 (15.29) | <0.001 |
| Rarely, n (SD) | 228 (14.25) | 188 (14.9) | 40 (11.76) | |
| Sometimes, n (SD) | 361 (22.57) | 304 (24.1) | 57 (17.76) | |
| Frequently, n (SD) | 378 (23.63) | 291 (23.1) | 87 (25.58) | |
| Very often, n (SD) | 308 (19.26 | 203 (16.2) | 104 (30.5) | |
| How many years have you smoked? | ||||
| I have never smoked, n (SD) | 872 (54.5) | 710 (56.39) | 162 (47.6) | <0.001 |
| ≤10 years, n (SD) | 244 (15.25) | 210 (16.67) | 34 (10) | |
| 11–20 years, n (SD) | 149 (9.31) | 119 (9.45) | 30 (8.82) | |
| 21–30 years, n (SD) | 107 (6.69) | 76 (6.03) | 31 (9.11) | |
| >30 years, n (SD) | 227 (14.19) | 144 (11.43) | 83 (24.41) | |
| How old are you? | ||||
| <40 years, n (SD) | 15 (0.93) | 15 (1.19) | 0 (0) | <0.001 |
| 40–49 years, n (SD) | 197 (12.32) | 176 (13.97) | 21 (6.17) | |
| 50–59 years, n (SD) | 320 (20.01) | 285 (822.63) | 35 (10.29) | |
| 60–69 years, n (SD) | 483 (30.2) | 387 (30.73) | 96 (28.23) | |
| ≥70 years, n (SD) | 584 (36.52) | 396 (31.45) | 188 (55.29 | |
| Total LFQ score, n (SD) | 16.2 (3.52) | 16.8 (3.34) | 14.1 (3.35) | <0.001 |
| LFQ development time, n (SD) | 0.9 (0.82) | 0.9 (0.87) | 0.8 (0.64) | 0.323 |
| LFQ score ≤18, n (SD) | 1161 (0.72) | 851 (9.67) | 310 (0.91) | <0.001 |
| LFQ score ≤18 without respiratory symptoms, n (SD) | 100 (0.41) | 79 (0.37) | 21 (0.80) | <0.001 |
| LFQ score ≤18 with respiratory symptoms, n (SD) | 1061 (0.78) | 772 (0.73) | 289 (0.92) | <0.001 |
| LFQ score ≤18 without smoking, n (SD) | 537 (0.62) | 401 (0.56) | 136 (0.85) | <0.001 |
| LFQ score ≤18 with smoking, n (SD) | 624 (0.85) | 450 (0.81) | 174 (0.96) | <0.001 |
| LFQ score ≤18 no exposure to wood smoke, n (SD) | 445 (0.67) | 353 (0.63) | 92 (0.87) | <0.001 |
| LFQ score ≤18 exposure to wood smoke, n (SD) | 716 (0.76) | 498 (0.70) | 218 (0.92) | <0.001 |
| LFQ score ≤18 no smoker in the house, n (SD) | 838 (0.75) | 595 (0.65) | 243 (0.91) | <0.001 |
| LFQ score ≤18 with smoker in the house, n (SD) | 201 (0.75) | 147 (0.71) | 54 (0.9) | 0.003 |
| LFQ score ≤18 no smoking or exposure to wood smoke, n (SD) | 182 (055) | 150 (0.52) | 32 (0.76) | 0.004 |
| LFQ score ≤18 with smoking and exposure to wood smoke, n (SD) | 361 (0.90) | 247 (0.87) | 114 (0.97) | 0.002 |
General characteristics of the population
| Total population, n = 1599 | Without COPD, n = 1259 | With COPD, n = 340 | p-value | |
|---|---|---|---|---|
| Age, in years, n (SD) | 65.3 (11.9) | 64 (11.88) | 70 (11.03) | <0.001 |
| Male sex, n (%) | 702 (49.9) | 518 (41.1) | 184 (54.1) | <0.001 |
| Race, n (%) | ||||
| White | 196 (12.2) | 153 (12.1) | 43 (12.5) | 0.354 |
| Half-blood | 1381 (86.4) | 1086 (86.2) | 295 (86.7) | |
| Black | 4 (3) | 3 (2.3) | 1 (0.2) | |
| Other | 3 (1) | 2 (0.2) | 1 (0.2) | |
| Educational level, n (SD) | ||||
| None | 20 (1.2) | 15 (1.2) | 5 (1.4) | <0.001 |
| Primary | 604 (37.7) | 425 (33.7) | 179 (52.6) | |
| High school | 427 (26.7) | 356 (28.2) | 71 (20.8) | |
| Technologist | 12 (0.77) | 11 (0.9) | 1 (0.2) | |
| Technical | 121 (9.3) | 29 (9.6) | 150 (8.5) | |
| Master's degree | 5 (0.3) | 2 (0.1) | 3 (0.8) | |
| Doctorate | 4 (0.2) | 4 (0.3) | 0 (0) | |
| Years of study, n (SD) | 9.3 (5.6) | 9.8 (5.56) | 7.5 (5.51) | <0.001 |
| Respiratory symptoms, n (%) | 1360 (85) | 1046 (83) | 314 (90) | <0.001 |
| Age at onset of symptoms, n (SD) | 57.3 (17.21) | 57 (16.11) | 57.5 (20.05) | 0.856 |
| Smoking, n (%) | 733 (45) | 553 (43) | 180 (52) | 0.003 |
| IPA, n (%) | 15.2 (23.26) | 12.8 (21.25) | 22.6 (27.43) | <0.001 |
| Passive smoker, n (%) | 266 (16) | 206 (16.2) | 60 (17.6) | 0.982 |
| Exposure to wood smoke, n (%) | 937 (58) | 702 (55.8) | 235 (69.1) | <0.001 |
| Prior diagnosis of COPD, n (%) | 409 (25) | 246 (19.5) | 163 (47.9) | <0.001 |
| Prior diagnosis of asthma, n (%) | 215 (13) | 149 (11.8)) | 66 (19.4) | <0.001 |
AUC of the LFQ questionnaire for COPD diagnosis
| AUC | 95% CI | p-value | |
|---|---|---|---|
| Total population of the study | 0.715 | 0.685–0.745 | <0.001 |
| Population without evidence of respiratory symptoms | 0.798 | 0.706–0.889 | <0.001 |
| Population with respiratory symptoms | 0.694 | 0.661–0.727 | <0.001 |
| Population without a history of smoking | 0.713 | 0.670–0.757 | <0.001 |
| Population with a history of smoking | 0.706 | 0.664–0.748 | <0.001 |
| Population without a history of exposure to wood smoke | 0.715 | 0.661–0.770 | <0.001 |
| Population with a history of exposure to wood smoke | 0.705 | 0.668–0.742 | <0.001 |
| Population without a history of smoking at home | 0.73 | 0.697–0.763 | <0.001 |
| Population with a history of smoking at home | 0.653 | 0.581–0.773 | <0.001 |
| Population without smoking and without exposure to wood smoke | 0.671 | 0.581–0.760 | <0.001 |
| Population with smoking and exposure to wood smoke | 0.674 | 0.617–0.730 | <0.001 |