In the period August 2005-August 2006, Boulware et al. (Boulware et al., 2006) conducted a national mail survey of 178 primary care providers (89 family physicians and 89 general internists; 28% response rate) and 126 nephrologists (39% response rate), identified with the American Medical Association Physician Masterfile. The questionnaire consisted of a hypothetical patient scenario, in which a primary care provider was evaluating a new patient with CKD stage 3 progressing to stage 4; the patient was identical for all cases (50-year-old female with creatinine values consistent with eGFR of 15-59 ml/min/1.73 m² and persistent proteinuria), except that her race/ethnicity (African-American or white) and comorbid illness status (hypertension only or hypertension with diabetes) varied by questionnaire. Physicians were asked to estimate the patient’s kidney function, and then were asked “How would you describe this patient’s kidney disease?” with possible responses of “normal or no kidney disease,” “mild kidney disease,” “moderate kidney disease,” “severe kidney disease,” and “end-stage kidney disease.” Responses of moderate or severe kidney disease were considered correct identification of CKD stage 3-4. Responding physicians were additionally asked: “Based on the information you know about this patient, do you recommend that the PCP refer the patient to a nephrologist at this time” with possible answers of “yes” or “no”.

As with all unweighted questionnaires the participants might not be representative of the targeted population.