Table 1—

Confounder/effect-modifier criteria for assessment of published chronic obstructive pulmonary disease (COPD) outcomes and markers

Brief description of variable
Has methodology been standardised?
Has the frequency distribution been establishedIn the general population?In COPD patients?
Is the variable reproducible?
Has the influence on the treatment been established?
Can the measure be performed during exacerbations of COPD?
Is the variable influencing common comorbidities, e.g. ischaemic heart disease, diabetes mellitus or psychiatric disturbances?
Can the variable be used in multicentre trials?
In order to measure the variable, what is needed?A questionnaireEquipmentTimeTraining
How much does the measurement of the variable cost?CheapModerateExpensive
Are there any safety issues?
Are there any ethical issues?
  • A confounder can be defined as a variable that can cause or prevent the outcome of interest, is not an intermediate variable and is associated with the factor under investigation. An effect modifier can be defined as a factor that modifies the effect of a putative causal factor under study.