Analytic Challenges with National Data 

Linked to State-Level Data 

The National Health Interview Survey – 

Florida Cancer Data System Linkage 

Eric A. Miller 

National Center for Health Statistics (NCHS) 
Pilot Project 

• Linkage of the Florida Cancer Data System 

(FCDS) Data to National Health Interview 

Survey (NHIS) 

• Objectives 

• Feasibility 

• Value / Utility 
Data Linkage 

National Health Interview 

Survey (1986 – 2009) + 

Dummy Records 

~2 Million Records 

Florida Cancer Data System 

(1981 – 2010)

~2.5 Million Records 

8,217 linked 

survey participants 
How Does This Apply to Other Linkages? 

• Some of the issues we have encountered 

with this linkage could be relevant for other 

National/State linkages 

• For example 

– State-level analysis of national survey data 

(e.g. NHIS) linked to Medicaid or 

Supplemental Nutrition Assistance Program 

(SNAP) 
Description of the Data 

• Cancer Registries 

– Collect, manage, and analyze data about 

cancer cases and cancer deaths 

– Are essential for monitoring progress in 

cancer prevention and control 
Data Collected by Cancer Registries 

• Cancer-related 

– Incident cancers 

– Type, extent (i.e. stage) and location of tumor 

– Date of diagnosis 

– Type of initial treatment 

• Demographics 

• Vital status 
Description of the Data 

• NHIS 

– In-person household survey 

– Conducted continuously by the CDC’s NCHS 

since 1957 

– Large sample sizes 

• ~35,000 households in the U.S. per year 

• Complex sampling with some populations 

oversampled 
Data Collected by NHIS 

• Risk factors (e.g. smoking, alcohol use, obesity) 

• Health conditions, diseases, and disabilities 

• Cancer screening history (selected years) 

• Occupation/Industry 

• Socioeconomic information (e.g. income, 

education, health insurance/access to care) 
Data Linkage 

• Linking the information from these two 

sources could potentially provide a valuable 

resource for cancer research 

• Linkage adds: 

– Longitudinal component to survey 

– Quality of life/health after diagnosis 

– Risk factor, SES, screening history, access to 

care, and comorbidity information to registry data 
Also Adds Complexity 

• NHIS is a nationally representative sample

of the civilian, non-institutionalized (CNI) 

population of the United States 

– i.e. not just Florida 

• FCDS is intended to capture (almost) all 

cancers diagnosed among Florida 

residents 
Examples of Challenges 

• Creation of survey weights 

• Survey participant mobility 
Challenge #1 – Survey Weights 

• NHIS weights were available to represent 

the US CNI population 

• Weights needed to be created to represent 

the Florida population 

– NCHS (Dean Judson) created weights to be 

representative of the Florida CNI population 

for each year of the survey
Creation of Florida Weights 

• Used NHIS sample weights 

– Limited to Florida survey participants 

– Adjusted for linkage ineligibility using PROC 

WTADJUST in SUDAAN 

• Based on race, sex and age 

– Linkage ineligibility 

• Did not refuse 

• Did not provide sufficient personally identifiable 

information 
Creation of Florida Weights 

• Post-stratified to the Florida CNI population 

Method 1: Using Florida CNI estimates directly 

from NHIS 

Method 2: Using estimates of the CNI 

population based on average CNI 

percent of total Florida population 

• Methods highly correlated (r=0.99) and 

had little effect on estimates 
Comparison 

Percent of survey participants with a cancer record in the FCDS 

who ever smoked by race/ethnicity, and post-stratification method 

Post-stratification

Method 1

Post-stratification 

Method 2 

Ever Smoked 

% (SE) 

Ever Smoked 

% (SE) 

Hispanic 48.2 (3.52) 48.0 (3.44)

White Non-Hispanic 63.9 (1.63) 64.1 (1.52)

Black Non-Hispanic 45.7 (3.33) 46.2 (3.23)
Consequence of Current Weighting 

Strategy 

• Participants are weighted to the CNI Florida 

population in the year of their survey 

• This means if you were interviewed in Minnesota 

but diagnosed with cancer in Florida, you get a 

weight of 0 

– Data for these respondents are not included in the 

analysis 

– Not a trivial number 
Challenge #2 - Movers 

• People moved to Florida after the survey 

– Some were diagnosed with cancer 

• In the FCDS 

– Some were not 

• Analytic implications 

– With current weighting strategy loss of sample 

size limits the ability to look at individual cancer 

types or at demographic differences 
Movers to Florida 

NHIS U.S. 

NHIS 

FL

Cancer 

dx in FL 

• Number of Survey 

Participants Linked 

to FCDS=8,217 
Movers to Florida 

NHIS U.S. 

NHIS 

FL

Cancer 

dx in FL 

• Number of Survey 

Participants Linked 

to FCDS=8,217 

• Number of FL 

survey participants 

linked to 

FCDS=6,366 
Movers to Florida 

NHIS U.S. 

NHIS 

FL

Cancer 

dx in FL 

• Number of Survey 

Participants Linked 

to FCDS=8,217 

• Number of FL 

survey participants 

linked to 

FCDS=6,366 

• Number who moved 

to FL after survey 

and were dx’d with 

cancer=1,851 (23%) 
Reason for Current Strategy 

Walter from MN 

Don - Florida Native 

Jack - MN Transplant 

If Walter moves to 

Florida and is dx’d 

with cancer, he is 

more comparable to 

Jack who moved to 

Florida and did not get 

cancer. 
Reason for Current Strategy 

Walter from MN 

Don - Florida Native 

Jack - MN Transplant 

But we do not have a 

way to know about 

Jack in the data. 
Comparison of Demographic Characteristics Among 

Participants Linked with FCDS by Residency at Survey 

Florida Residents 

% 

Movers 

% 

Male* 49.6 52.7

Race/Ethnicity*

White 83.6 91.8

Black 14.3 5.8

Hispanic 21.0 5.5

Mean Age (as of 2009)* 61.3 56.7

Education Level*

< High School (HS) 7.0 14.0

HS Graduate 45.3 46.3

> HS 47.7 39.7

*P<0.05 for difference between groups 
Comparison of Health Characteristics Among 

Participants Linked with FCDS by Residency at Survey 

Florida Residents 

% 

Movers 

% 

Smoking Status*

Never 40.0 33.0

Current 23.5 27.7

Former 36.3 39.3

Self-rated Health*

Excellent / Very Good / Good 76.3 85.0

Fair / Poor 23.7 15.0

*P<0.05 for difference between groups 
Comparison of Cancer Types Among Participants 

Linked with FCDS by Residency at Survey 

Cancer

Florida Residents 

%** 

Movers 

%** 

Bladder 6.2 6.2

Breast (Female)* 19.0 15.4

Colorectal 12.8 12.4

Lung 13.8 13.4

Prostate 18.6 20.0

Thyroid 1.5 1.2

Uterus 3.6 2.7

*P<0.05 for difference between groups 

**Percent of all cancer diagnoses. Cancer types are not mutually exclusive and 

table does not include all categories. Not intended to add up to 100%. 
Alternate Weighting Strategy 

• Statistical matching 

– For movers (in-migration) find a similar survey 

participant from Florida and split weight between 

Florida and non-Florida resident 

– Could limit to those diagnosed with cancer within 

a certain number of years (e.g. with 5 years of 

survey) 

– Could base magnitude of split on number of years 

between survey and diagnosis in Florida 

• e.g. 5 years: 90% FL /10% not FL, 1 year: 50%/50% 
Challenge #2B: Movers Out of Florida 

• People moved out of Florida after the 

survey 

– Some were diagnosed with cancer 

– Some were not 
Movers Out of Florida 

• Change of address data are available to 

see who moved from Florida 

– But we do not have a way to identify survey 

participants who were diagnosed with cancer 

in another state 

• This would require linkages with cancer registries 

nationally 
Movers Out of Florida 

• Analytic implications 

• Can affect the representativeness of the estimates if a 

sizeable number of participants moved out of state 

• Currently do not have a way to address movers out of 

state 
Conclusions 

• Linking national survey data to state-level 

data produces additional analytic 

considerations 

– And opportunities for further research 

• When linking national and state-level data, 

it is important to consider the potential 

impact of “movers” 
Co-Authors/Collaborators 

• NCHS

– Donna Miller 

– Dean Judson 

– Hannah Day 

– Yulei He 

– Jennifer Parker 

• FCDS/University of 

Miami 

– Cristina Fernandez 

– Monique Hernandez 

– Jill MacKinnon 

– Laura McClure 

– Brad Wohler 

– Recinda Sherman 

– Bill LeBlanc 

– Sharon Christ 

– David Lee 
For More Information 

Eric Miller: bwe6@cdc.gov 

Data Linkage at NCHS: 

datalinkage@cdc.gov 

www.cdc.gov/nchs/data_access/data_linkage_activities.htm 

Thanks!