National Health Interview Survey
NHIS at a Glance
| National Health Interview Survey | |
|---|---|
| Data Type | National self-report survey |
| Sample | Nationally representative sample |
| VEHSS Topics Included | Visual Function |
| Years Analyzed | 2014, 2015 merged |
| Approximate Size | 87,500 people per year |
The main objective of the National Health Interview Survey (NHIS) is to monitor the health of the United States population through the collection and analysis of data on a broad range of health topics. The survey has been conducted since 1957, and since 1960 has been conducted by National Center for Health Statistics (NCHS). NHIS data are used widely by the Department of Health and Human Services (DHHS) and the public health research community to monitor trends in illness and disability and to track progress toward achieving national health objectives. NHIS was selected for inclusion in VEHSS due to its wide range of vision-related questions, as well as its inclusion of all three risk factor variables of interest.
Sample Design
The NHIS is a cross-sectional household interview survey of the noninstitutionalized US population. Each year, the sample contains approximately 35,000 households and 87,500 individuals. Sampling and interviewing occurs continuously throughout the year. The sampling plan follows a multistage area probability design that permits the representative sampling of households and noninstitutional group quarters (e.g., college dormitories). The sampling plan is redesigned after every decennial census.
The first stage of the 2006–2015 sampling plan consists of selecting a sample of 428 primary sampling units (PSU’s) drawn from approximately 1,900 geographically defined PSU’s that cover the 50 states and the District of Columbia. Nearly all states have at least two PSUs selected for the sample, with most having notably more. For each PSU, there are two second-stage units—area segments which are defined geographically, and permit segments which cover housing units built after the 2000 census. The NHIS sampling frame consists of the area and permit frames, which consist of all of the area and permit segments, respectively. This sampling design includes the oversampling of black, Asian, and Hispanic people.
The total NHIS sample is subdivided into four separate panels, or sub-designs, such that each panel is a representative sample of the US population. For 2006–2010, the households and noninstitutional group quarters selected for interview each week are a probability sample representative of the target population. Beginning in 2011, the minimum time length for a probability sample changed from a week to a month.
Data Collection Procedures
NHIS data are collected via an in-person household interview conducted by interviewers who are employed and trained by the US Census Bureau. Since 1997, the NHIS questionnaire has been administered in the computer assisted personal interviewing (CAPI) mode. The questionnaire is administered with a laptop computer, with interviewers entering responses directly during the interview.
For the family core component, all adult members of the household who are 18 years or older and at home during the time of the interview are invited to participate and respond for themselves. If a child or adult is not home during the interview, a responsible adult family member who is 18 years or older and resides in the household can provided the answers. For the Sample Adult questionnaire, one civilian adult per family is randomly selected to be interviewed. Similarly, a child is randomly selected for the Sample Child questionnaire. Information for this questionnaire is provided by an adult knowledgeable about the child’s health.[1]
In 2015, the final response rate for the sample adult component was 55.2%. In 2015, the final response rate for the sample child component was 63.4%. In 2014, the final response rate for the sample adult component was 58.9% and for the sample child component was 66.6%. For a combined 2014-2015, the sample adult final response rate was 57.1% and the sample child final response was 65.0%.
For VEHSS, NORC estimated the prevalence rate and sample size for each survey instrument selected for inclusion. We merged samples from the 2014 and 2015 rounds for analysis in order to maximize the available sample sizes at more detailed levels of stratification. New weights were created by dividing the original weights by two.1
For binary response questions included in the analysis, prevalence rate was defined as the number of people who gave an affirmative response to the question divided by the total number of respondents who gave an affirmative or negative response and then multiplied by 100 for presentation in percentage format. For scaled responses, the data value is the proportion of respondents that selected one of the possible response option, and all responses should sum to 100%. We estimated upper and lower confidence intervals and the relative standard error (RSE) of the prevalence estimate using the Clopper-Pearson method.[2] Estimates that were based on a sample size less than 30 and/or with a RSE greater than 30% were suppressed.
A detailed description of the analytical steps is described in the report “VEHSS Survey Analysis Plan Cdc-pdf[PDF – 480 KB]External.” Full analysis documentation is included in the “VEHSS NSCH Data Report Cdc-pdf[PDF – 568 KB]External.”
Variables Analyzed in VEHSS
There were six vision-related questions during 2014–2015 period across all NHIS core and supplemental questionnaires. All six questions were categorized under the VEHSS ‘Visual Function’ Topic. Two questions were categorized under the VEHSS ‘Blind of Difficulty Seeing’ category, three were categorized under ‘Difficulty Seeing with Glasses,’ and one under ‘Vision Correction.’ The questions came from three questionnaires—sample child, sample adult, and functioning and disability. The functioning and disability questionnaire was administered to approximately half of the adult sub-sample, via random selection.
Only child participants who responded ‘Yes’ to CVISION question were asked the CBLIND question. Similarly, only adult participants who responded ‘Yes’ to the AVISION question were asked the ABLIND question. Question wording for all questions was consistent across both 2014 and 2015.
Overview of NHIS Variables Included in VEHSS
| VEHSS Indicator Topic | VEHSS Indicator Category | NHIS Variable Name | Years Available (analyzed) |
NHIS Question Text | Response Options |
|---|---|---|---|---|---|
| Sample Child File | |||||
| Visual Function | Blind or Difficulty Seeing | CBLIND | 1999–2016 (2014–15 merged) |
Is [NAME] blind or unable to see at all? | 1 Yes |
| Visual Function | Difficulty Seeing with Glasses | CVISION | 1999–2016 (2014–15 merged) |
Does [NAME] have any trouble seeing, even when wearing glasses or contact lenses? |
|
| Sample Adult File | |||||
| Visual Function | Blind or Difficulty Seeing | ABLIND | 1999–2016 (2014–15 merged) |
Are you blind or unable to see at all? |
|
| Visual Function | Difficulty Seeing with Glasses | AVISION | 1999–2016 (2014–15 merged) |
Do you have any trouble seeing, even when wearing glasses or contact lenses? |
|
| Functioning and Disability File | |||||
| Visual Function | Difficulty Seeing with Glasses | VIS_SS | 2011–2015 (2014–15 merged) |
Do you have difficulty seeing, even when wearing glasses? |
|
| Visual Function | Vision Correction | VIS_0 | 2012–2015 (2014–15 merged) |
Do you wear glasses? |
|
The NHIS data analyzed are limited in a few ways. NHIS does not publicly release state-level data, and therefore only national level data is included in VEHSS. All responses are self-reported, or household reported in the case of children. The self-report measures represent indicators that cannot be directly translated into the prevalence of clinically defined visual impairment or blindness. Finally, the questions included in NHIS are not present in other surveys, and therefore are not directly equivalent to any other survey indicator measures included in VEHSS.
Additional information about NHIS can be found on the CDC website.
[1] US Department of Health and Human Services. Centers for Disease Control and Prevention. National Center for Health Statistics. (2016). 2015 National health Interview Survey (NHIS) Public Use Data Release: Survey Description. Retrieved from: ftp://ftp.cdc.gov/pub/Health_Statistics/NCHS/Dataset_Documentation/NHIS/2015/srvydesc.pdf
[2] Parker JD, Talih M, Malec DJ, et al. (2017). National Center for Health Statistics Data Presentation Standards for Proportions. National Center for Health Statistics. Vital Health Stat 2(175).