DATA PREPARATION AND PROCESSING PROCEDURES                       
                                                                                
                                                                                
Automated data collection procedures for the survey were introduced in          
NHANES III.  In the mobile examination centers, data for the interview and      
examination components were recorded directly onto a computerized data          
collection form.  With the exception of a few independently automated           
systems, the system was centrally integrated.  This operation allowed for       
ongoing monitoring of much of the data.  Before the introduction of the         
computer-assisted personal interview (CAPI), the household questionnaire        
data were reviewed manually by field editors and interviewers.  CAPI            
(1992-1994 only) questionnaires featured built-in edits to prevent entering     
inconsistencies and out-of-range responses.  The multi-level data               
collection and quality control systems are discussed in detail in the Plan      
and Operation of the Third National Health and Nutrition Examination Survey,    
1988-1994 (NCHS, 1994; U.S. DHHS, 1996).  All interview, laboratory, and        
examination data were sent to NCHS for final processing.                        
                                                                                
Guidelines were developed that provided standards for naming variables,         
filling missing values and coding conventional responses, handling missing      
records, and standardizing two-part quantity/unit questionnaire variables.      
NCHS staff, assisted by contract staff, developed data editing                  
specifications that checked data sets for valid codes, ranges, and skip         
pattern consistencies and examined the consistency of values between            
interrelated variables.  Comments, collected in both interviews and             
examination components, were reviewed and recoded when possible.  Responses     
to "Other" and "Specify" were recoded either to existing code categories or     
to new categories.  The documentation for each data set includes notes for      
those variables that have been recoded and standardized and for those           
variables that differ significantly from what appears in the original data      
collection instrument.  While the data have undergone many quality control      
and editing procedures, there still may be values that appear extreme or        
illogical.  Values that varied considerably from what was expected were         
examined by analysts who checked for comments or other responses that might     
help to clarify unusual values.  Generally, values were retained unless they    
could not possibly be true, in which case they were changed to "Blank but       
applicable."  Therefore, the user must review each data set for extreme or      
inconsistent values and determine the status of each value for analysis.        
                                                                                
Several editing conventions were used in the creation of final analytic         
data sets:                                                                      
                                                                                
1.   Standardized variables were created to replace all two-part                
     quantity/unit questions using standard conversion factors.                 
     Standardized variables have the same name as the variable of the           
     two-part question with an "S" suffix.  For instance, MAPF18S (Months       
     received WIC benefits) in the MEC Adult Questionnaire was created from     
     the two-part response option to question F18, "How long did you receive    
     benefits from the WIC program?," using the conversion factor 12 months     
     per year.                                                                  
                                                                                
2.   Recoded variables were created by combining responses from two or more     
     like variables, or by collapsing responses to create a summary             
     variable for the purpose of confidentiality.  Recoded variables have the   
     original variable name with an R suffix.  For example, place of birth      
     variable (HFA6X) in the Family Questionnaire was collapsed to a three      
     level response category (U.S., Mexico, Other) and renamed HFA6XR.          
     Generally, only the recoded variable has been included in the data file.   
                                                                                
                                                                               
3.   Fill values, a series of one or more digits, were used to represent        
     certain specific conditions or responses.  Below is a list of the fill     
     values that were employed.  Some of the fill values pertain only to        
     questionnaire data, although 8-fill and blank-fill values are found in     
     all data sets.  Other fill values, not included in this list, are used     
     to represent component-specific conditions.                                
                                                                                
     6-fills = Varies/varied. (Questionnaires only)                             
                                                                                
     7-fills = Fewer than the smallest number that could be reported within     
     the question structure (e.g., fewer than one cigarette per day).           
     (Questionnaires only)                                                      
                                                                                
     8-fills = Blank but applicable/cannot be determined.  This means that      
     a respondent was eligible to receive the question, test, or component      
     but did not because of refusal, lack of time, lack of staff, loss of       
     data, broken vial, language barrier, unreliability, or other similar       
     reasons.                                                                   
                                                                                
     9-fills = Don't know.  This fill was used only when a respondent did       
     not know the response to a question and said, "I don't know."              
     (Questionnaires only)                                                      
                                                                                
     Blank fills = Inapplicable.  If a respondent was not eligible for a        
     questionnaire, test, or component because of age, gender, or specific      
     reason, the variable was blank-filled.  In the questionnaire, if a         
     respondent was not asked a question because of a skip-pattern,             
     variables corresponding to the question were blank-filled.  For            
     examination or laboratory components, if a person was excluded by a        
     defined protocol (e.g., screening exclusion questions) and these           
     criteria are included in the data set, then the corresponding              
     variables were blank-filled for that person.  For home examinees,          
     variables for examination components and blood tests not performed as      
     part of the home examination protocol were blank-filled.                   
                                                                                
4.   For variables describing discrete data, codes of zero (0) were used to     
     mean "none," "never," or the equivalent.  Value labels for which "0"       
     is used include:  "has not had," "never regularly," "still taking," or     
     "never stopped using."  Unless otherwise labeled, for variables            
     containing continuous data, "zero" means "zero.                            
                                                                                
5.   Where there are logical skip patterns in the flow of the questionnaire     
     or examination component, the skip was indicated by placing the            
     variable label of the skip destination in parentheses as part of the       
     value label of the response generating the skip.  For example, in the      
     Physical Function Evaluation, the variable PFPWC (in wheelchair) has a     
     value label, "2  No (PFPSCOOT)" that means that the next item for          
     persons not in a wheelchair would be represented by the variable,          
     PFPSCOOT.                                                                  
                                                                                
                                                                                
Variable Nomenclature                                                           
                                                                                
A unique name was assigned to every NHANES III variable using a standard        
convention.  By following this naming convention, the origin of each            
variable is clear, and there is no chance of overlaying similar variables       
across multiple components.  Variables range in length from three to eight      
characters.  The first two variable characters represent the topic (e.g.,       
analyte, questionnaire instrument, examination component) and are listed        
below alphabetically by topic.  For questionnaires administered in the          
household, the remainder of the variable name following the first two           
                                                                               
characters indicates the question section and number.  For example, data        
for the response to the Household Adult Questionnaire question B1 are           
contained in the variable HAB1.  For most laboratory and examination            
variables, as well as some other variables, a "P" in the third position         
refers to "primary" and the remainder of the variable name is a brief           
description of the item.  For instance, in the Laboratory Data File,            
information on the length of time the person fasted before the first blood      
draw is contained in the variable PHPFAST.  The variable PHPFAST was derived    
as follows:  characters 1-2 (PH) refer to "phlebotomy," character 3 (P)         
refers to "primary," characters 4-8 (FAST) refer to an abbreviation for         
"fasting."                                                                      
                                                                                
                                                                                
CODE           TOPIC                                                            
                                                                                
AT             Alanine aminotransferase (from biochemistry profile)             
AM             Albumin (from biochemistry profile)                              
AP             Alkaline phosphatase (from biochemistry profile)                 
AL             Allergy skin test                                                
AC             Alpha carotene                                                   
AN             Anisocytosis                                                     
AA             Apolipoprotein (AI)                                              
AB             Apolipoprotein (B)                                               
AS             Aspartate aminotransferase (from biochemistry profile)           
LA             Atypical lymphocyte                                              
AU             Audiometry                                                       
BA             Band                                                             
BO             Basophil                                                         
BS             Basophilic stippling                                             
BC             Beta carotene                                                    
BX             Beta cryptoxanthin                                               
BL             Blast                                                            
BU             Blood urea nitrogen (BUN) (from biochemistry profile)            
BM             Body measurements                                                
BD             Bone densitometry                                                
C1             C-peptide (first venipuncture)                                   
C2             C-peptide (second venipuncture)                                  
CR             C-reactive protein                                               
UD             Cadmium                                                          
CN             Central nervous system function evaluation                       
CL             Chloride (from biochemistry profile)                             
CO             Cotinine                                                         
CE             Creatinine (serum)(from biochemistry profile)                    
UR             Creatinine (urine)                                               
DM             Demographic                                                      
DE             Dental examination                                               
MQ             Diagnostic interview schedule                                    
DR             Dietary recall (total nutrient intakes)                          
EO             Eosinophil                                                       
EP             Erythrocyte protoporphyrin                                       
FR             Ferritin                                                         
FB             Fibrinogen                                                       
RB             Folate (RBC)                                                     
FO             Folate (serum)                                                   
FH             Follicle stimulating hormone (FSH)                               
FP             Fundus photography                                               
                                                                                
                                                                               
CODE           TOPIC                                                            
                                                                                
GG             Gamma glutamyl transferase (GGT) (from biochemistry profile)     
GU             Gallbladder ultrasonography                                      
GB             Globulin (from biochemistry profile)                             
G1             Glucose (first venipuncture)                                     
G2             Glucose (second venipuncture)                                    
SG             Glucose (from biochemistry profile)                              
GH             Glycated hemoglobin                                              
GR             Granulocyte                                                      
C3             HCO3 (Bicarbonate)(from biochemistry profile)                    
HD             HDL cholesterol                                                  
HP             Helicobacter pylori antibody                                     
HT             Hematocrit                                                       
HG             Hemoglobin                                                       
AH             Hepatitis A antibody (HAV)                                       
HB             Hepatitis B core antibody (anti-HBc)                             
SS             Hepatitis B surface antibody (anti-HBs)                          
SA             Hepatitis B surface antigen (HBsAg)                              
HC             Hepatitis C antibody (HCV)                                       
DH             Hepatitis D antibody (HDV)                                       
H1             Herpes 1 antibody                                                
H2             Herpes 2 antibody                                                
HX             Home examination (general)                                       
HF             Household family questionnaire                                   
HA             Household adult questionnaire                                    
HQ             Household questionnaire variables (composite)                    
HS             Household screener questionnaire                                 
HY             Household youth questionnaire                                    
HZ             Hypochromia                                                      
I1             Insulin (first venipuncture)                                     
I2             Insulin (second venipuncture)                                    
UI             Iodine (urine)                                                   
FE             Iron                                                             
SF             Iron (from biochemistry profile)                                 
LD             Lactate dehydrogenase (from biochemistry profile)                
L1             Latex antibody                                                   
LC             LDL cholesterol (calculated)                                     
PB             Lead                                                             
LP             Lipoprotein (a)                                                  
LH             Luteinizing hormone                                              
LU             Lutein/zeaxanthin                                                
LY             Lycopene                                                         
LM             Lymphocyte                                                       
MR             Macrocyte                                                        
MC             Mean cell hemoglobin (MCH)                                       
MH             Mean cell hemoglobin concentration (MCHC)                        
MV             Mean cell volume (MCV)                                           
PV             Mean platelet volume                                             
MA             MEC adult questionnaire                                          
MX             MEC examination (general)                                        
FF             Dietary food frequency (ages 12-16 years)                        
MP             MEC proxy questionnaire                                          
MY             MEC youth questionnaire                                          
ME             Metamyelocyte                                                    
MI             Microcyte                                                        
MO             Monocyte                                                         
MN             Mononuclear cell                                                 
ML             Myelocyte                                                        
                                                                                
                                                                               
CODE           TOPIC                                                            
                                                                                
IC             Normalized calcium (derived from ionized calcium)                
OS             Osmolality (from biochemistry profile)                           
PH             Phlebotomy data collected in MEC (e.g., questions)               
PS             Phosphorus (from biochemistry profile)                           
PF             Physical function evaluation                                     
PE             Physician's examination                                          
PL             Platelet                                                         
DW             Platelet distribution width                                      
PK             Poikilocytosis                                                   
PO             Polychromatophilia                                               
SK             Potassium (from biochemistry profile)                            
PR             Promyelocyte                                                     
RC             Red blood cell count (RBC)                                       
RW             Red cell distribution width (RDW)                                
RE             Retinyl esters                                                   
RF             Rheumatoid factor antibody                                       
RU             Rubella antibody                                                 
WT             Sample weights                                                   
SE             Selenium                                                         
SI             Sickle cell                                                      
NA             Sodium (from biochemistry profile)                               
SH             Spherocyte                                                       
SP             Spirometry                                                       
SD             Survey design                                                    
TT             Target cell                                                      
TE             Tetanus                                                          
TB             Total bilirubin (from biochemistry profile)                      
CA             Total calcium                                                    
SC             Total calcium (from biochemistry profile)                        
TC             Total cholesterol                                                
CH             Total cholesterol (from biochemistry profile)                    
TI             Total iron binding capacity (TIBC)                               
TP             Total protein (from biochemistry profile)                        
TX             Toxic granulation                                                
TO             Toxoplasmosis antibody                                           
PX             Transferrin saturation                                           
TG             Triglycerides                                                    
TR             Triglycerides (from biochemistry profile)                        
TY             Tympanometry                                                     
UA             Uric acid (from biochemistry profile)                            
UB             Urinary albumin                                                  
VU             Vacuolated cells                                                 
VR             Varicella antibody                                               
VA             Vitamin A                                                        
VB             Vitamin B12                                                      
VC             Vitamin C                                                        
VE             Vitamin E                                                        
WC             White blood cell count (WBC)                                     
WW             WISC/WRAT cognitive test