Table 3.
—Mixed-Effects Linear Regression Model for SGRQ Total Score Using Exacerbation Frequency in the Prior Year (N = 1,255)
| Predictor Variable and Level | Estimate | SE | P Value |
| Pack-y smoking history | 0.066 | 0.014 | < .001 |
| Age, y | −0.256 | 0.048 | < .001 |
| Annual exacerbation rate race interaction | |||
| African American | 1.887 | 0.688 | .006 |
| Caucasian | Ref | … | … |
| Annual exacerbation rate | 1.928 | 0.327 | < .001 |
| FEV1 % predicted | −0.111 | 0.019 | < .001 |
| Sex | |||
| Female | −1.486 | 0.705 | .04 |
| Male | Ref | … | … |
| MMRC dyspnea score | 8.489 | 0.310 | < .001 |
| Race | |||
| African American | −0.672 | 1.213 | .58 |
| Caucasian | Ref | … | … |
| 6-min walk distance, m | −0.026 | 0.004 | < .001 |
| Education level | |||
| More than HS | −4.805 | 1.139 | < .001 |
| Graduated HS | −2.919 | 1.206 | < .001 |
| Less than HS | Ref | … | … |
| Current smoking | |||
| Yes | 2.754 | 0.817 | < .001 |
| No | Ref | … | … |
This mixed-effects linear regression model included clinical center as a random effect to account for possible regional and other differences. Clinical center did affect SGRQ total score (P < .001). Of the 1,273 subjects in GOLD stages I to IV, six subjects did not answer the question about current smoking, and 12 subjects did not answer the questions from which the MMRC dyspnea score was derived. As a result, 1,255 subjects were used in this regression analysis. GOLD = Global Initiative for Obstructive Lung Disease; Ref = referent group. See Table 1 and 2 legends for expansion of other abbreviations.