The dataset we have chosen for this book is part of the National Hospital Ambulatory Medical Care Survey (NHAMCS) public use data. It is survey data published and maintained by the US Center for Disease Control and Prevention (CDC). The home page for this data set is https://www.cdc.gov/nchs/ahcd/ahcd_questionnaires.htm.
- The NHAMCS data is survey-based data; it is populated by surveys sent to patients and healthcare providers that were seen in the hospital for encounters.
- The data files are in fixed-width format. In other words, they are text files in which each row is on a distinct line, and columns are each a set number of characters long. Information about the character length of each feature is available in the corresponding NHAMCS documentation.
- There are different sets of files depending on whether the data is from outpatient encounters or emergency department visits. We will be using the ED format in this chapter.
- The data comes with detailed documentation about the content of each feature.
- Each row of the data represents a distinct ED patient encounter.
See the following table for a summary of the emergency department data files from NHAMCS that we will be using throughout this book:
| Filename | Data type and year | Number of rows (encounters) | Number of columns (features) | Broad feature categories |
| ED2013 | ED Encounters; 2013 | 24,777 | 579 | Visit date and information, Demographics, Tobacco, Arrival means, Payment, Vital signs, Triage, ED relationship, Reason for visit, Injury, Diagnoses, Chronic conditions, Services performed, Providers seen, Disposition, Hospital admission, Imputed data, ED information, Socioeconomic data |