D (dyspnoea), a two-level factor with levels yes
and no.
T (tuberculosis), a two-level factor with levels
yes and no.
L (lung cancer), a two-level factor with levels
yes and no.
B (bronchitis), a two-level factor with levels
yes and no.
A (visit to Asia), a two-level factor with levels
yes and no.
S (smoking), a two-level factor with levels yes
and no.
X (chest X-ray), a two-level factor with levels
yes and no.
E (tuberculosis versus lung cancer/bronchitis), a
two-level factor with levels yes and no.