Depression was measured using the Patient Health Questionnaire (PHQ-9), a nine-item screening instrument that asks questions about the frequency of symptoms of depression over the past 2 weeks. A final follow-up question assesses the overall impairment of the depressive symptoms. Response categories "not at all," "several days," "more than half the days" and "nearly every day" were given a score ranging from 0 to 3. A total score was calculated ranging from 0 to 27. A score of 10 or higher has been well validated and is commonly used in clinical studies to define depression. Other methods for defining depression based on this instrument are also used.
Mobile examination center participants 12 years and older were eligible. Due to risk of disclosure, data for 12-17 year olds was not included in the publicly released data file (DPQ).This limited access data file contains only the youth data.
Interview Setting and Mode of Administration
The Depression screener was asked at the mobile examination center, by trained interviewers, using the Computer-Assisted Personal Interviewing (CAPI) system as part of the Mobile Examination Center (MEC) interview in Spanish or English. No proxy or interpreters were permitted for these questions.
Quality Assurance & Quality Control
The CAPI system is programmed with built-in consistency checks to reduce data entry errors. CAPI also uses online help screens to assist interviewers in defining key terms used in the questionnaire.
Approximately 5% of the interviews were recorded and reviewed for quality control purposes.
Data Processing and Editing
Edits were made to ensure the completeness, consistency and analytic usefulness of the data.
Depression and depression severity have been defined using various methods in the scientific literature. Researchers may want to pay special attention to records with item non-response (questions that have missing, "don't know" or "refusal" responses) in deriving a score or severity measure.
MEC exam sample weights should be used for the analyses.
Please refer to the NHANES Analytic Guidelines
and the on-line NHANES Tutorial
for further details on the use of sample weights and other analytic issues.