Physician's prescribing preference as an instrumental variable: exploring assumptions using survey data

Background: Physician's prescribing preference is increasingly used as an instrumental variable in studies of therapeutic effects. However, differences in prescribing patterns among physicians may reflect differences in preferences or in case-mix. Furthermore, there is debate regarding the possible assumptions for point estimation using physician's preference as an instrument. Methods: A survey was sent to general practitioners (GPs) in The Netherlands, the United Kingdom, New Zealand, Ireland, Switzerland, and Germany, asking whether they would prescribe levothyroxine to eight fictitious patients with subclinical hypothyroidism. We investigated (1) whether variation in physician's preference was observable and to what extent it was explained by characteristics of GPs and their patient populations and (2) whether the data were compatible with deterministic and stochastic monotonicity assumptions. Results: Levothyroxine prescriptions varied substantially among the 526 responding GPs. Between-GP variance in levothyroxine prescriptions (logit scale) was 9.9 (95% confidence interval: 8.0, 12) in the initial mixed effects logistic model, 8.3 (6.7, 10) after adding a fixed effect for country and 8.2 (6.6, 10) after adding GP characteristics. The occurring prescription patterns falsified the deterministic monotonicity assumption. All cases in all countries were more likely to receive levothyroxine if a different case of the same GP received levothyroxine, which is compatible with the stochastic monotonicity assumption. The data were incompatible with this assumption for a different definition of the instrument. Conclusions: Our study supports the existence of physician's preference as a determinant in treatment decisions. Deterministic monotonicity will generally not be plausible for physician's preference as an instrument. Depending on the definition of the instrument, stochastic monotonicity may be plausible

Patient and physician gender concordance in preventive care in university primary care settings

Background: The proportion of female physicians working in primary care medicine has increased for several decades. Several studies have reported physician gender differences in preventive health care received by patients, especially for gender-specific preventive services. However, limited data exist on the role of patient and physician gender and gender concordance in the broad spectrum of preventive care. Therefore, we assessed the association between physician gender, patient-physician gender concordance, and the quality of preventive care in Swiss university primary care settings. Methods: We performed a retrospective cohort study of 1001 randomly selected patients aged 50-80 years from four Swiss university primary care settings. We used indicators derived from RAND’s Quality Assessment Tools indicators and calculated percentages of recommended preventive care (such as behavioral counseling and cancer screening) according to physician and patient gender. We used a hierarchical multivariate logistic regression, adjusting for patients’ age and occupation, and for physicians’ age, function and centre (both as random factors). Results: 1001 patients (mean age 63.5 years, 557 male) were followed by 189 physicians (mean age 34.2 years, 90 male, 94.7% residents). After multivariate adjustment, female patients received less recommended preventive care than male patients (88.4% vs. 91.3%, p<0.001). Female physicians provided significantly more preventive care than male physicians (p=0.04) to both female (88.8% vs. 87.7%) and male patients (91.6% vs. 90.7%). We found no evidence that preventive care differed among gender concordant and discordant patient-physician pairs (p for interaction = 0.78). Female physicians provided particularly more recommended cancer screening (colon cancer, breast cancer) than male physicians (81.2% vs. 75.3%, p=0.01). Conclusion: In Swiss primary care settings, female patients receive less preventive care than male patients. Furthermore, female physicians provide significantly more preventive care than their male colleagues, particularly for cancer screening. This study suggests that greater attention should be paid to female patients in preventive health care. Further studies are needed to understand why female physicians tend to provide better preventive care

International variation in GP treatment strategies for subclinical hypothyroidism in older adults: a case-based survey

Background: There is limited evidence about the impact of treatment for subclinical hypothyroidism, especially among older people. Aim: To investigate the variation in GP treatment strategies for older patients with subclinical hypothyroidism depending on country and patient characteristics. Design and setting: Case-based survey of GPs in the Netherlands, Germany, England, Ireland, Switzerland, and New Zealand. Method: The treatment strategy of GPs (treatment yes/no, starting-dose thyroxine) was assessed for eight cases presenting a woman with subclinical hypothyroidism. The cases differed in the patient characteristics of age (70 versus 85 years), vitality status (vital versus vulnerable), and thyroid-stimulating hormone (TSH) concentration (6 versus 15 mU/L). Results: A total of 526 GPs participated (the Netherlands n = 129, Germany n = 61, England n = 22, Ireland n = 21, Switzerland n = 262, New Zealand n = 31; overall response 19%). Across countries, differences in treatment strategy were observed. GPs from the Netherlands (mean treatment percentage 34%), England (40%), and New Zealand (39%) were less inclined to start treatment than GPs in Germany (73%), Ireland (62%), and Switzerland (52%) (P = 0.05). Overall, GPs were less inclined to start treatment in 85-year-old than in 70-year-old females (pooled odds ratio [OR] 0.74 [95% confidence interval [CI] = 0.63 to 0.87]). Females with a TSH of 15 mU/L were more likely to get treated than those with a TSH of 6 mU/L (pooled OR 9.49 [95% CI = 5.81 to 15.5]). Conclusion: GP treatment strategies of older people with subclinical hypothyroidism vary largely by country and patient characteristics. This variation underlines the need for a new generation of international guidelines based on the outcomes of randomised clinical trials set within primary car