Table 2.

Examples of instrumental variables recently used in published studies

Association examined	Instrumental variable	Reference
NSAID treatment for persistent ductus arteriosus and mortality and moderate/severe bronchopulmonary dysplasia	Institutional variation in NSAID treatment frequency	Slaughter et al53
Nonparental childcare attendance and childhood obesity	The number of relatives who live close to the family	Isong et al54
Use of NIV in patients with pneumonia and 30-day mortality	Differential distance, ie, the difference between 1) the distance from a patient’s residence to the nearest high NIV use hospital and 2) the distance from a patient’s residence to the nearest hospital of any type	Valley et al55
Psychosocial assessment of patients in the emergency department and risk of repeat self-harm	Time of day of hospital presentation	Carroll et al56
Second-generation versus third-generation oral contraceptives and risk of venous thromboembolism	Proportion of prescriptions for third-generation oral contraceptives by the general practitioner in the year preceding the current prescription	Boef et al57
Readmission destination and risk of mortality after major surgery	Regional index hospital readmission rates	Brooke et al58

Abbreviations: NIV, noninvasive ventilation; NSAID, non-steroidal anti-inflammatory drug.