Table 4

Sensitivity analysis

ParameterNew cases (per 100 targeted)Rate difference (per 100 targeted)% additional cases detected with active approachNNTProportion of expected cases in the community detected with active approach
ActiveOpportunistic only
Base case3.82.21.670%630.49
Model assumptions
Proportion with any respiratory symptom
COPD* in those with respiratory symptoms
Process assumptions
Questionnaire response rate (postal)
GP asks questionnaire in surgery
Spirometry uptake rate
Spirometry accuracy
0.9 sensitivity3.42.01.470%700.44
0.8 sensitivity3.01.81.370%790.39
  • Numbers in bold are referred to in the text.

  • * Clinically significant COPD defined as respiratory symptoms and airways obstruction (National Institute for Health and Clinical Excellence criteria).

  • COPD, chronic obstructive pulmonary disease; GP, general practitioner; NNT, number needed to target with the active approach to identify one additional new case over opportunistic only.