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 |
|
| Years Analyzed | 2014/15 merged, 2016/17 merged |
| Approximate Size | Approximately 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 National Health Interview Survey 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 was redesigned most recently in 2016.
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 U.S. 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.
2016-2018 Sampling Plan
A new sample design was implemented with the 2016 NHIS. Sample areas were reselected to take into account changes in the distribution of the U.S. population since 2006, when the previous sample design was first implemented. Commercial address lists were used as the main source of addresses, rather than field listing; and the oversampling procedures for Black, Hispanic, and Asian persons that were a feature of the previous sample design were not implemented in 2016.
The first stage of the current sample design consists of a sample of 319 primary sampling units (PSUs) drawn from approximately 1,700 geographically defined PSUs, with some PSUs in each of the 50 states and the District of Columbia.
The NHIS sampling frame consists of three non-overlapping parts: the unit frame (a list of addresses purchased from a vendor); the area frame (geographic areas that do not have city-style addresses, and geographic areas where the unit frame was not considered to be a sufficient sampling resource); and the college dormitory frame (college residence hall spaces in the NHIS sample PSUs). As with the earlier sample designs, the total NHIS sample is subdivided into four separate panels such that each panel is representative of the U.S. civilian noninstitutionalized population (as is any combination of the four panels).
Data Collection Procedures
NHIS data are collected via an in-person household interview conducted by interviewers who are employed and trained by the U.S. 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 Household Composition section, one household member who is at least the age of legal majority for the state of residence is identified as the household respondent. The household respondent provides basic demographic and relationship information about all household members; these relationships determine the number of families that comprise the household. For the Family core component, all adult members of the household who are 18 years and older and at home during the time of the interview are invited to participate and respond for themselves, however a family respondent may respond for all children and adults in the family. 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 provide 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]
We estimated the prevalence rate and sample size for each survey instrument selected for inclusion. We merged samples from the 2014 and 2015 rounds and then the 2016 and 2017 rounds for analysis in order to maximize the available sample sizes at more detailed levels of stratification. This partition corresponds to the new sampling frame, as well as more vision-related questions were fielded in 2016-2017. New weights were created by dividing the original weights by two [2].
For binary response questions included in the analysis, prevalence rate was defined as the number of persons 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 any 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 of the prevalence estimate using the Clopper-Pearson method with the smaller of the effective sample size and the sample size. The respondent sample size was reported for each response.
All estimates were calculated using SAS proc survey freq. Suppression was determined using the National Center for Health Statistics Data Presentation Standards for Proportions released in August 2017 [3].
A detailed description of the analytical steps is described in the report “VEHSS Survey Analysis Plan [PDF – 480 KB]external icon.” Full analysis documentation is included in the “VEHSS NSCH Data Report [PDF – 568 KB]external icon.”
Variables Analyzed in VEHSS
Across all the NHIS core and supplemental questionnaires, there were 16 vision-related questions during 2014-2015 period. For the 2016-2017 period, there were 46 vision-related questions. Many of these questions are duplicative of one another, as the same question may be asked of two different target populations—e.g., children and adults–in two different questionnaires. For the 2014-2015 analyses, we prioritized the six questions that provide an understanding of the prevalence of visual impairment in children and adults. For the 2016-2017 analyses, with the increase in the number of questions, we included questions from the child and adult sample files that asked about service utilization in addition to those that provide an understanding of the prevalence of visual impairment. Questions we have not yet included in these analyses focus on access to vision-related healthcare and aids and duration of vision problems.
Child Questionnaire
We analyzed eight questions from the child sample file, six of those questions are asked with the same or very similar wording in the adult sample questionnaire. Two of the questions were asked all four years while the other six were only asked in 2016-2017. Five questions were categorized under the ‘Service Utilization’ Topic and three under the ‘Visual Function’ Topic. Each ‘Visual Function’ Topic question fell into its own category –‘Blind of Difficulty Seeing’, ‘Difficulty Seeing with Glasses,’ and ‘Vision Correction’.
Adult Sample Questionnaire
We analyzed 18 questions from the adult sample file, covering three Topics areas – ‘Visual Function’, ‘Eye Health Conditions’, and ‘Service Utilization’. Six of the nine ‘Visual Function’ questions asked about difficulty performing a range of routine activities and fell into the ‘Far-Distance Visual Function’, ‘Night Vision’, ‘Miscellaneous Life Impact’, ‘Near-Distance Visual Function’, and ‘Peripheral Visual Function’ categories. The other three ‘Visual Function’ questions each fell into their own categories– ‘Difficulty Seeing with Glasses’, “Blind or Difficulty Seeing’, and ‘Vision Correction’. The four ‘Eye Health Conditions’ questions asked respondents whether a doctor ever told them they had diabetic retinopathy, cataracts, glaucoma, or macular degeneration. The five ‘Service Utilization’ question were related to eye exam with dilation, cataract surgery, use of eye protection when participating in potential eye-injury-causing activities, and interacting with an eye health provider. The functioning and disability questionnaire was administered to approximately half of the adult sub-sample, via random selection through 2017. In 2018 the functioning and disability questions are being asked to the entire adult sample. Table 1 presents additional details about these questions, including the VEHSS Topic and Category, the NHIS variable name, the year(s) survey data are available, the survey question, and the response options. The table also includes the universe included in the question as there were several questions that had follow-up questions if the response was ‘Yes’ to the main question.
Table 1. NHIS Variables analyzed in VEHSS
| VEHSS Indicator Topic | VEHSS Indicator Category | NHIS Variable Name | Years Available1 | Question | Universe | Response Options |
|---|---|---|---|---|---|---|
| Sample Child File | ||||||
| Visual Function | Blind or Difficulty Seeing | CVISION | 1999-2018 | Does [NAME] have any trouble seeing, even when wearing glasses or contact lenses? | Sample children <18 | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Visual Function | Blind of Difficulty Seeing | CBLIND | 1999-2018 | Is [NAME] blind or unable to see at all? | Sample children <18 who said Yes to CVISION | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Service Utilization | Eye Exams | CVISTST | 2016-2017 | Has [NAME] EVER had [his/her] vision tested by a doctor or other health professional? | Sample children <6 who are not blind | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Service Utilization | Eye Exams | CVISLT | 2016-2017 | When was [his/her] vision last tested? | Sample children <6 who said Yes to CVISTST | 1 in the last 12 month 2 in the last 13-24 months 3 Over 24 months 7 Refused 8 Not ascertained 9 Don’t know |
| Visual Function | Vision Correction | CVISGLAS | 2016-2017 | Does [NAME] wear eyeglasses or contact lenses? | Sample children 6-17 who are not blind | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Service Utilization | Use of eye protection | CVISACT | 2016-2017 | Does [NAME] participate in sports, hobbies, or other activities that can cause eye injury? This includes activities such as baseball, basketball, soccer and mowing the lawn. | Sample children 6-17 | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Service Utilization | Use of eye protection | CVISPROT | 2016-2017 | When doing these activities, on average, does [he/she] wear eye protection always, most of the time, some of the time, or none of the time? | Sample children 6-17 who said YES to CVISACT | 1 Always 2 Most of the time 3 Some of the time 4 None of the time 7 Refused 8 Not ascertained 9 Don’t know |
| Service Utilization | Eye Health Provider Interaction | CHCSYR11
CHCSYR2 |
2016-2018 | DURING THE PAST 12 MONTHS, has anyone in the family seen or talked to any of the following health care providers about [NAME]’s health?
An optometrist, ophthalmologist, or eye doctor (someone who prescribes eyeglasses)? |
Sample children <18 | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Sample Adult File | ||||||
| Visual Function | Difficulty Seeing with Glasses | AVISION | 1999–2016 | Do you have any trouble seeing, even when wearing glasses or contact lenses? | Sample Adult 18+ | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Visual Function | Blind of Difficulty Seeing | ABLIND | 1999–2016 | Are you blind or unable to see at all? | Sample adults 18+ who said Yes to AVISION | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Eye Health Conditions | Self-Report Diabetic Retinopathy | VIM_DREV | 2016-2017 | Have you EVER been told by a doctor or other health professional that you had Diabetic retinopathy? | Sample Adult 18+ | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Eye Health Conditions | Self-Report Cataract | VIM_CAEV | 2016-2017 | Have you EVER been told by a doctor or other health professional that you had Cataracts? | Sample Adult 18+ | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Service Utilization | Cataract Surgery | VIMCSURG | 2016-2017 | Have you ever had cataract surgery? | Sample Adult 18+ who said Yes to VIM_CAEV | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Eye Health Conditions | Self-Report Glaucoma | VIM_GLEV | 2016-2017 | Have you EVER been told by a doctor or other health professional that you had glaucoma | Sample Adult 18+ | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Eye Health Conditions | Self-Report Age Related Macular Degeneration | VIM_MDEV | 2016-2017 | Have you EVER been told by a doctor or other health professional that you had Macular Degeneration? | Sample Adult 18+ | 1 Yes 2 No 7 Refused 8 Not ascentained 9 Don’t know |
| Visual Function | Vision Correction | VIMGLASS | 2016-2017 | Do you currently wear eyeglasses or contact lenses? | Sample Adult 18+ who said No to ABLIND | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Visual Function | Far-Distance Visual Function | AVDF_NWS | 2016-2017 | Even when wearing glasses or contacts lenses, because of your eyesight, / Fill 2: Because of your eyesight,] how difficult is it for you
…To read ordinary print in newspapers |
Sample Adult 18+ who said No to ABLIND | 0 Not at all difficult 1 Only a little difficult 2 Somewhat difficult 3 Very difficult 4 Can’t do at all because of eyesight 6 Do not do this activity for other reasons 8 Not ascertained 9 Don’t know |
| Visual Function | Far-Distance Visual Function | AVDF_CLS | 2016-2017 | Even when wearing glasses or contacts lenses, because of your eyesight, / Fill 2: Because of your eyesight,] how difficult is it for you
…To do work or hobbies require you to see well up close such as cooking, sewing, fixing things around the house or using hand tools |
Sample Adult 18+ who said No to ABLIND | 0 Not at all difficult 1 Only a little difficult 2 Somewhat difficult 3 Very difficult 4 Can’t do at all because of eyesight 6 Do not do this activity for other reasons 8 Not ascertained 9 Don’t know |
| Visual Function | Night Vision | AVDF_NIT | 2016-2017 | Even when wearing glasses or contacts lenses, because of your eyesight, / Fill 2: Because of your eyesight,] how difficult is it for you
…To go down steps, stairs, or curbs in dim light or at night |
Sample Adult 18+ who said No to ABLIND | 0 Not at all difficult 1 Only a little difficult 2 Somewhat difficult 3 Very difficult 4 Can’t do at all because of eyesight 6 Do not do this activity for other reasons 8 Not ascertained 9 Don’t know |
| Visual Function | Miscellaneous Life Impact | AVDF_CRD | 2016-2017 | Even when wearing glasses or contacts lenses, because of your eyesight, / Fill 2: Because of your eyesight, ] how difficult is it for you
…To find something on a crowded shelf |
Sample Adult 18+ who said No to ABLIND | 0 Not at all difficult 1 Only a little difficult 2 Somewhat difficult 3 Very difficult 4 Can’t do at all because of eyesight 6 Do not do this activity for other reasons 8 Not ascertained 9 Don’t know |
| Visual Function | Near-Distance Visual Function | AVDF_DRV | 2016-2017 | Even when wearing glasses or contacts lenses, because of your eyesight, / Fill 2: Because of your eyesight,] how difficult is it for you
…To drive during daytime in familiar places |
Sample Adult 18+ who said No to ABLIND | 0 Not at all difficult 1 Only a little difficult 2 Somewhat difficult 3 Very difficult 4 Can’t do at all because of eyesight 6 Do not do this activity for other reasons 8 Not ascertained 9 Don’t know |
| Visual Function | Peripheral Visual Function | AVDF_PER | 2016-2017 | Even when wearing glasses or contacts lenses, because of your eyesight, / Fill 2: Because of your eyesight,] how difficult is it for you
…To notice objects off to the side while you are walking along |
Sample Adult 18+ who said No to ABLIND | 0 Not at all difficult 1 Only a little difficult 2 Somewhat difficult 3 Very difficult 4 Can’t do at all because of eyesight 6 Do not do this activity for other reasons 8 Not ascertained 9 Don’t know |
| Service Utilization | Eye Exams | AVISEXAM | 2016-2017 | When was the last time you had an eye exam in which the pupils were dilated? This would have made you temporarily sensitive to bright light. | Sample Adult 18+ who said No to ABLIND | 1 Less than one month 2 1-12 months 3 13-24 months 4 More than 2 years 5 Never 7 Refused 8 Not ascertained 9 Don’t know |
| Service Utilization | Use of eye protection | AVISACT | 2016-2017 | Outside of work, do you participate in sports, hobbies, or other activities that can cause eye injury? This includes activities such as baseball, basketball, mowing the lawn, wood working, or working with chemicals. | Sample Adult 18+ | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Service Utilization | Use of eye protection | AVISPROT | 2016-2017 | When doing these activities, on average, do you wear eye protection always, most of the time, some of the time, or none of the time? | Sample Adult 18+ who said Yes to AVISACT | 1 Always 2 Most of the time 3 Some of the time 4 None of the time 7 Refused 8 Not ascertained 9 Don’t know |
| Service Utilization | Eye Health Provider Interaction | AHCSYR2 | 2016-2018 | DURING THE PAST 12 MONTHS, have you seen or talked to any of the following health care providers about your own health?
…An optometrist, ophthalmologist or eye doctor (someone who prescribes eyeglasses). |
Sample Adult 18+ | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
| Functioning and Disability File | ||||||
| Visual Function | Difficulty Seeing with Glasses | VIS_SS22 | 2011-2018 | Do you have difficulty seeing, even when wearing glasses? | Sample adults 18+ who were asked the family disability questions (FDB) and were randomly selected to receive the Functioning and Disability (AFD) section | 1 No difficulty 2 Some difficulty 3 A lot of difficulty 4 Cannot do at all/unable to do 7 Refused 8 Not ascertained 9 Don’t know |
| Visual Function | Vision Correction | VIS_02 | 2012–2018 | Do you wear glasses? | Sample adults 18+ who were asked the family disability questions (FDB) and were randomly selected to receive the Functioning and Disability (AFD) section | 1 Yes 2 No 7 Refused 8 Not ascertained 9 Don’t know |
Table 2 presents the sample sizes for analysis by coded response option for the variables included in this report. The 2016-2017 functioning and disability questions were used for internal validation purposes.
| Variable | Response | Sample Size |
|---|---|---|
| Sample Child File | ||
| CVISION CBLIND |
Yes | 655 (CBLIND Yes 31, No 621, Missing 3) |
| No | 24,988 | |
| Missing | 28 | |
| CHCSYR11 CHCSYR2 |
Not analyzed | Not analyzed |
| Sample Adult File | ||
| AVISION ABLIND |
Yes | 7202 (ABLIND Yes 309, No 6,890, Missing 3) |
| No | 63,130 | |
| Missing | 37 | |
| Functioning and Disability File | ||
| VIS_SS2 | No difficulty | 27,894 |
| Some difficulty | 4,842 | |
| A lot of difficulty | 605 | |
| Cannot do at all/unable to do | 69 | |
| Refused | 73 | |
| Not ascertained | 1,741 | |
| Don’t know | 18 | |
| VIS_0 | Yes | 2,099 |
| No | 12,429 | |
| Missing | 1,823 | |
| Variable | Response | Sample Size |
|---|---|---|
| Sample Child File | ||
| CVISION CBLIND |
Yes | 661 (CBLIND Yes 30, No 631, Missing 0) |
| No | 19,270 | |
| Missing | 21 | |
| CVISTST CVISLT | Yes | 2997 (CVISLT In the last 12 months 2,492, In the last 13-24 months 357, Over 24 months 126, Don’t Know 22, Missing 0) |
| No | 3,367 | |
| Missing | 103 | |
| CVISGLAS | Yes | 4,472 |
| No | 8,981 | |
| Missing | 2 | |
| CVISACT CVISPROT |
Yes | 5,943 (CVISPROT Always 1,020, Most of the time 418, Some of the time 676, None of the time 3,812, Refused 1, Don’t know 16, Missing 0) |
| No | 7,527 | |
| Missing | 9 | |
| CHCSYR11 CHCSYR2 | Yes | 5,455 |
| No | 14,386 | |
| Missing | 111 | |
| Sample Adult File | ||
| AVISION ABLIND |
Yes | 7,030 (ABLIND Yes 265, No 6,765, Missing 0) |
| No | 52,721 | |
| Missing | 0 | |
| VIM_DREV | Yes | 613 |
| No | 59,067 | |
| Missing | 90 | |
| VIM_CAEV VIMCSURG |
Yes | 10,767 (VIMCSURG Yes 6,467, No 59,067, Missing 4) |
| No | 48,935 | |
| Missing | 68 | |
| VIM_GLEV | Yes | 1,996 |
| No | 57,687 | |
| Missing | 87 | |
| VIM_MDEV | Yes | 1,480 |
| No | 58,174 | |
| Missing | 116 | |
| VIMGLASS | Yes | 40,379 |
| No | 19,117 | |
| Missing | 274 | |
| AVDF_NWS | Not at all difficult | 47,881 |
| Only a little difficult | 6,474 | |
| Somewhat difficult | 3,161 | |
| Very difficult | 1,274 | |
| Can’t do at all because of eyesight | 318 | |
| Do not do this activity for other reasons | 370 | |
| Refused | 8 | |
| Not ascertained | 0 | |
| Don’t know | 19 | |
| Missing | 265 | |
| AVDF_CLS | Not at all difficult | 50,819 |
| Only a little difficult | 4,704 | |
| Somewhat difficult | 2,343 | |
| Very difficult | 829 | |
| Can’t do at all because of eyesight | 222 | |
| Do not do this activity for other reasons | 551 | |
| Refused | 9 | |
| Not ascertained | 0 | |
| Don’t know | 28 | |
| Missing | 265 | |
| AVDF_NIT | Not at all difficult | 52,206 |
| Only a little difficult | 3,062 | |
| Somewhat difficult | 1,987 | |
| Very difficult | 975 | |
| Can’t do at all because of eyesight | 200 | |
| Do not do this activity for other reasons | 1,044 | |
| Refused | 12 | |
| Not ascertained | 0 | |
| Don’t know | 19 | |
| Missing | 265 | |
| AVDF_CRD | Not at all difficult | 55,612 |
| Only a little difficult | 1,964 | |
| Somewhat difficult | 1,080 | |
| Very difficult | 409 | |
| Can’t do at all because of eyesight | 92 | |
| Do not do this activity for other reasons | 310 | |
| Refused | 12 | |
| Not ascertained | 0 | |
| Don’t know | 26 | |
| Missing | 265 | |
| AVDF_DRV | Not at all difficult | 53,527 |
| Only a little difficult | 1,161 | |
| Somewhat difficult | 1,987 | |
| Very difficult | 194 | |
| Can’t do at all because of eyesight | 282 | |
| Do not do this activity for other reasons | 3,781 | |
| Refused | 11 | |
| Not ascertained | 0 | |
| Don’t know | 14 | |
| Missing | 265 | |
| AVDF_PER | Not at all difficult | 55,824 |
| Only a little difficult | 1,619 | |
| Somewhat difficult | 999 | |
| Very difficult | 419 | |
| Can’t do at all because of eyesight | 156 | |
| Do not do this activity for other reasons | 418 | |
| Refused | 11 | |
| Not ascertained | 0 | |
| Don’t know | 59 | |
| Missing | 265 | |
| AVISEXAM | Less than one month | 3,445 |
| 1-12 months | 23,577 | |
| 13-24 months | 9,520 | |
| More than 2 years | 15,322 | |
| Never | 7,149 | |
| Refused | 20 | |
| Not ascertained | 0 | |
| Don’t know | 737 | |
| Missing | 0 | |
| AVISACT AVISPROT | Yes | 14,842 (AVISPROT Always 4,770, Most of the time 2,291, Some of the time 2,850, None of the time 4,918, Refused 1, Not ascertained 0, Don’t know 3) |
| No | 44,908 | |
| Missing | 20 | |
| AHCSYR2 | Yes | 26,544 |
| No | 32,549 | |
| Missing | 677 | |
| Functioning and Disability File | ||
| VIS_SS2 | No difficulty | 24,289 |
| Some difficulty | 4,060 | |
| A lot of difficulty | 414 | |
| Cannot do at all/unable to do | 49 | |
| Refused | 26 | |
| Not ascertained | 954 | |
| Don’t know | 11 | |
| VIS_0 | Yes | 19,616 |
| No | 9,211 | |
| Missing | 976 | |
Stratification Variables
All variables from the sample child file (CVISION, CBLIND, CVISTST, CVISLT, CVISGLAS, CVISACT, CVISPROT, and CHCSYR11/CHCSYR2 ) were stratified by age, sex, and race/ethnicity. The variables from the sample adult (AVISION, ABLIND, VIM_DREV, VIM_CAEV, VIMSURG, VIM_GLEV, VIM_MDEV, VIMGLASS, AVDF_NWS, AVDF_CLS, AVDF_NIT, AVDF_CRD, AVDF_DRV, AVDF_PER, AVISEXAM, AVISACT, AVISPROT, AHCSYR2) and 2014-2015 functioning and disability files (VIS_SS2, VIS_0) were stratified by age, sex, and race/ethnicity, diabetes status, hypertension status, and smoking status. Ages (variable: AGE_P) ranged from 0 to 17 years for participants in the sample child file, and from 18 to 85+ in the sample adult and functioning and disability files. Participant sex (variable: SEX) was coded as Male or Female. The Hispanic and race variables (variables: HISPAN_I and RACERPI2) were combined to create a single race/ethnicity variable, with anyone identifying as Hispanic being placed in a single category. The race categories were coded as follows: Non-Hispanic Asian, Non-Hispanic Black, Hispanic, Non-Hispanic North American Native, Non-Hispanic Other, and Non-Hispanic White. The ‘Other’ category consists of those whose race was not releasable due to issues of confidentiality, as well as those who identify with multiple racial categories. Diabetes status (variable: DIBEV) was recoded into ‘Yes,’ ‘No,’ and ‘Borderline’; Hypertension status (HYPEV) as ‘Yes’ and ‘No’; and Smoking status (SMKSTAT2) as ‘Current,’ ‘Former,’ and ‘Never.’ State identifiers are not released in NHIS public use files due to confidentiality concerns. Stratification variables and their frequencies are listed below.
| Variables | Frequency | ||||
|---|---|---|---|---|---|
| 2014-2015 | 2016-2017 | ||||
| Sample Child File | Sample Adult File | Functioning and Disability File | Sample Child File | Sample Adult File | |
| AGE | |||||
| 0-17 years | 25671 | – | – | 19952 | – |
| 18-39 years | 24069 | 12009 | 19226 | ||
| 40-64 years | – | 29278 | 14649 | – | 24308 |
| 65-84 years | – | 14774 | 7440 | – | 14190 |
| 85 years and older | – | 2248 | 1144 | – | 2046 |
| SEX | |||||
| Male | 13137 | 31469 | 15778 | 10351 | 27087 |
| Female | 12534 | 38900 | 35242 | 9601 | 32683 |
| RACE/ETHNICITY | |||||
| Non-Hispanic White | 11928 | 43634 | 21844 | 10983 | 41720 |
| Non-Hispanic Black | 3475 | 9359 | 4660 | 2272 | 6397 |
| Hispanic, any race | 7342 | 11644 | 5843 | 4390 | 7050 |
| Asian | 11928 | 3907 | 1960 | 1080 | 2919 |
| Non-Hispanic Other | 1227 | 1309 | 671 | 1016 | 1176 |
| North American Native | 222 | 516 | 264 | 211 | 508 |
| DIABETES | |||||
| Yes | – | 7471 | 3717 | – | 6331 |
| Borderline | – | 1183 | 598 | – | 1679 |
| No | – | 61670 | 30904 | – | 51706 |
| Missing | – | 45 | 23 | – | 54 |
| HYPERTENSION | |||||
| Yes | – | 24141 | 12204 | – | 21054 |
| No | – | 46138 | 22995 | – | 38631 |
| Missing | – | 90 | 43 | – | 85 |
| SMOKING | |||||
| Current Smoker | – | 11793 | 5836 | – | 9355 |
| Former Smoker | – | 16060 | 8045 | – | 14754 |
| Never Smoker | – | 42185 | 21188 | – | 35438 |
| Missing | – | 331 | 173 | – | 223 |
Stratification Levels Included in the Full Analysis
The full analysis includes additional stratifications beyond those included in this data summary report, and will be made available on the VEHSS project website. We stratified data using all possible combinations of age, race/ethnicity, sex, and risk factor at the national level. All stratifications are displayed in Table 4.
| Stratification Level | Stratification Factor |
|---|---|
| 0-level | All participants |
| 1-level | Age |
| Race/Ethnicity | |
| Sex | |
| Diabetes | |
| Hypertension | |
| Smoking | |
| 2-level | Age* Race/Ethnicity |
| Age*Sex | |
| Race/Ethnicity *Sex | |
| Age*Diabetes | |
| Age*Hypertension | |
| Age*Smoking | |
| Race/Ethnicity *Diabetes | |
| Race/Ethnicity *Hypertension | |
| Race/Ethnicity *Smoking | |
| Sex*Diabetes | |
| Sex*Hypertension | |
| Sex*Smoking | |
| 3-level | Age* Race/Ethnicity *Sex |
| Age* Race/Ethnicity *Diabetes | |
| Age* Race/Ethnicity *Hypertension | |
| Age* Race/Ethnicity *Smoking | |
| Age*Sex*Diabetes | |
| Age*Sex*Hypertension | |
| Age*Sex*Smoking | |
| Race/Ethnicity *Sex*Diabetes | |
| Race/Ethnicity *Sex*Hypertension | |
| Race/Ethnicity *Sex*Smoking | |
| 4-level | Age* Race/Ethnicity *Sex*Diabetes |
| Age* Race/Ethnicity *Sex*Hypertension | |
| Age* Race/Ethnicity *Sex*Smoking |
The NHIS data analyzed are limited in a few ways. NHIS does not publicly release state-level data, and therefore only national level data will be 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, many of the new vision questions included in the 2016 and 2017 NHIS are not present in the 2018 and 2019 surveys nor in surveys within a similar time frame, making it difficult to compare across surveys or across years.
Please see the full VEHSS NHIS data analysis report for additional details on the analysis and validation of the VEHSS analysis of the NHIS.
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).