Statistical analysis
Descriptive statistics were used to examine distributions
and determine levels of all key variables (means and SDs for continuous variables, proportions for categoric). Differences in demographic characteristics, appraisal, and coping between patients with and without psychological distress were examined using chi-square analyses, with the exception of using the nonparametric Mann Whitney U test for two variables with skewed distributions: disease severity (FEV1) and perceived stress intensity. Logistic regression for the development of psychological distress was then performed using only
the factors that were significantly different between
groups (selected items of the WOC) as predictors,
after testing for multicollinearity, and controlled for
possible confounders (demographic characteristics
and disease severity). Odds ratios were estimated, and 95% confidence intervals were determined. All
statistical analysis were performed using SPSS Version
11 for Windows (SPSS Inc, Chicago, IL); all tests
were two tailed with alpha set at P _ .05.