Methods
We analyzed data from the outpatient department subset of the NHAMCS, which is administered annually by the National Center for Health Statistics at the Centers for Disease Control and Prevention and is designed to collect data on the use and provision of ambulatory care services in hospital emergency and outpatient departments. The NHAMCS uses a 4-stage probability sampling procedure to collect nationally representative data. Physicians and hospital staff are trained to complete patient record forms for visits randomly selected via a systematic selection procedure during a 4-week period. The activities of physicians, nurse practitioners/certified midwives (referred to as nurse practitioners in this article), and physician assistants are recorded in this database. Data on demographic characteristics, symptoms, diagnosis of chronic conditions, vital signs, diagnostic and screening services provided, health education provided, treatments implemented, and provider type are collected for each patient on the patient record form. Detailed information about the sampling design and data collection for the NHAMCS is available at http://www.cdc.gov/nchs/ahcd/about_ahcd.htm. Because this study was a secondary analysis of public data from the Centers for Disease Control and Prevention, institutional review board approval was not sought.
We used NHAMCS outpatient department data from 5 years (2005–2009); we selected these 5 years because the items used to collect the data were identical across survey years during that period. Data on 162,012 outpatient department visits during this time were abstracted; we excluded 25,580 visits for the following reasons: the patient made a visit for a new, undiagnosed condition, made a presurgery or a postsurgery visit, or was younger than 18 years, or the visit included care by more than 1 provider type (any combination of physician, physician assistant, and nurse practitioner).
We included in our analysis visits at which a diagnosis of asthma, chronic obstructive pulmonary disease (COPD), depression, diabetes, hyperlipidemia, hypertension, ischemic heart disease, or obesity was recorded (in NHAMCS question 5a). We also included visits if any of these 8 diagnoses were selected from among the 14 chronic conditions listed in question 5b, "Regardless of the diagnoses written in 5a, does the patient now have …" (www.cdc.gov/nchs/data/ahcd/nhamcs100opd_2009.pdf). A list of health education needs for each chronic condition (Box) was developed by using national and international treatment guidelines, and providers were credited for delivering health education if they documented it in the patient record. Health education was considered to have been provided if it was delivered by the provider or if the provider directed another health professional such as a nurse, social worker, or registered dietician to deliver it during the same visit. Health education provided during a different visit was not included in the analysis because NHAMCS has no mechanism for collecting this information.
Our final sample consisted of 136,432 records. For each type of health education, we determined the number of patient visits for each type of provider (physician, physician assistant, and nurse practitioner) and computed the percentage of patients who received education by provider type. We used logistic regression models to compute odds ratios and to obtain a statistical test of the null hypothesis that the percentage of patients receiving the indicated type of health education did not vary across provider types. All estimates and P values were obtained by using methods that adjust for unequal sampling weights as well as stratification and clustering in the sampling design. We used Stata version 12 (StataCorp LP, College Station, Texas) for all analyses.