Body Mass Index (BMI)
MODULE INFORMATION
PURPOSE OF THE MODULE:
To monitor Body Mass Index to assess the impact of of healthy eating and exercise
strategies on body weight.
MODULE HISTORY:
Added to the original survey in 2001
The height and weight of respondents has been collected in RRFSS since 2001. The
respondent may provide the data in empirical (feet, inches, pounds) or metric (centimetres,
kilograms) measurements.
From 2001 to 2006, calculation of BMI was done at the health unit level, with the exception
of 2002 when derived variables for metric height and weight, BMI and the BMI categories
were included in the dataset. There are errors in the 2002 derived variables for some
respondents so these should not be used.
Beginning in 2007, ISR added calculations in the CATI to convert empirical responses to
metric and to calculate BMI (bmi_ISR), and also added a derived variable for the BMI
categories (bmicat_ISR) to the dataset.
DATA DICTIONARY HISTORY:
Created: September 2002
Revised: February 2003; June 2013: Changed to new data dictionary template. Added
CATI calculated and post-CATI derived variable information. Revised the indicator to
overweight and obese adults 18+ (previously age 20-64). June 2014: Revised the indicator
to note changes to the use of the derived variables bmi_ISR and bmi1_ISR.
Rapid Risk Factor Surveillance System (RRFSS)
Body Mass Index (BMI)
MODULE QUESTIONS
VARIABLE NAME: bmi1
VARIABLE HISTORY:
Added January 2001 (Wave 1)
QUESTION:
How tall are you without shoes?
Response Options
bmi1feet
bmi1inch
bmi1cent
998
999
height in feet
height in inches
height in centimetres
don’t know
refused
ANALYSIS ISSUES:
 The response is entered in either feet and inches or centimeters
 In 2001-2002 don’t know and refused responses were coded as 98 & 99 respectively
for bmi1feet, bmi1inch & bmi1cent so these values should be set to missing when
calculating BMI
 bmi1feet and bmi1inch are set to 0 as default
 bmi1cent was set to 0 as default only in 2001-2002
 The range of valid values for bmi1feet is 3-9 feet
 The range of valid values for bmi1inch is 0-11 inches
 The range of valid values for bmi1cent is 90-300 centimetres
 Starting in 2007 the variables hgt_cm (height in centimetres) and hgt_m (height in
metres) are calculated in CATI and since 2010 have been included in the dataset. In
2008, 2009 and 2012 the variable htmetre (the rounded value of hgt_m) is also
included in the dataset.
COMPARABILITY TO OTHER SURVEYS:
CCHS (2000/01) Cycle 1.1: HW_Q2 –
How tall are you without shoes on?
NPHS (1996/97): HTWT-Q2, HWC6_2 –
How tall are you without shoes on?
BRFSS (2002): #12.11 p18 –
About how tall are you without shoes?
VALIDITY/RELIABILITY TESTS:
Reliability generally better than validity. Self reported height tends to be over estimated (&
weight under-estimated) – therefore BMI under-estimated) Nelson et al. 2001. Self-reports
are useful, cost-effective way to monitor changes in BMI, but percentage estimates of BMI
are relative rather than absolute.
EVALUATION QUESTIONS: None
Rapid Risk Factor Surveillance System (RRFSS)
Body Mass Index (BMI)
MODULE QUESTIONS
VARIABLE NAME: bmi2
VARIABLE HISTORY:
Added January 2001 (Wave 1)
QUESTION:
How much do you weigh?
Response Options
bmi2lbs
bmi2kilo
998
999
weight in pounds
weight in kilograms
don’t know
refused
ANALYSIS ISSUES:
 The response is entered in either pounds or kilograms
 bmi2lbs is set to 0 as default except in 2001-2002
 The range of valid values for bmi2lbs is 70-575 pounds
 The range of valid values for bmi2kilo is 35-260 kilograms
 Starting in 2007 the variable wgt_kg (weight in kilograms) is calculated in CATI and
since 2010 has been included in the dataset. In 2008, 2009 and 2012 the variable
wtkilo (the rounded value of wgt_kg) is also included in the dataset.
COMPARABILITY TO OTHER SURVEYS:
CCHS (2000/01) Cycle 1.1: HW_Q3 –
How much do you weigh?
NPHS (1996/97): HTWT-Q2, HWC6_2 –
How much do you weigh?
BRFSS (2002): #12.10 p18 –
How much do you weigh without shoes?
VALIDITY/RELIABILITY TESTS:
Reliability is generally better than validity. Since self-reported height tends to be overestimated and self-reported weight under-estimated, BMI tends to be under-estimated
(Nelson et al. 2001). Self-reports are a useful, cost-effective way to monitor changes in
BMI, but percentage estimates of BMI are relative rather than absolute.
EVALUATION QUESTIONS: None
Rapid Risk Factor Surveillance System (RRFSS)
Body Mass Index (BMI)
MODULE DERIVED VARIABLES
DERIVED VARIABLE NAME: bmicat_ISR
DERIVED VARIABLE DESCRIPTION:
Body Mass Index (BMI) – 4 categories
Variable Label: Body Mass Index, Age 18+, Canadian Standard 2003
Value of bmicat_ISR
1
2
3
4
0
Value Label
Underweight (<18.5)
Acceptable Weight (18.5-24.9)
Overweight (25.0-29.9)
Obese (>=30.0)
Preg / hgt lt 36in or hgt gt 83in /DK / Ref
* bmicat_ISR=0 is set to missing
YEAR FIRST INCLUDED IN ANNUAL DATA SET: 2007
Note: the 2002 dataset includes derived variables for height (htmetre), weight (wtkilo), BMI
(bmi) and the BMI categories (bmicat) but there are errors in these variables for some
respondents so they should not be used.
VARIABLES USED TO COMPUTE DERIVED VARIABLE: bmi_ISR
 bmicat_ISR is the body mass index calculated in CATI since 2007 based on a
respondent’s height and weight using the formula: weight in kilograms (wgt_kg) /
(height in meters (hgt_m)*height in metres (hgt_m)).
 bmicat_ISR is not calculated if a respondent is pregnant, refuses to answer or
answers don’t know to the height or weight questions, or their height is less than 3’
or greater than 6’11” (hgt_m >= 0.91 or hgt_m <= 2.11).
 calculation in CATI:
[store <0> in bmi_ISR]
[if rh1 gt <1> or rh1 eq <>][#not pregnant]
[if HGT_M ge <0.91> and HGT_M le <2.11>]
[store (WGT_KG/HGT_M/HGT_M) in bmi_ISR]
[endif]
[endif]
 bmicat_ISR has been included in the dataset since 2007. bmi1_ISR was included
in the dataset from 2009 until 2013, and was derived by truncating bmi_ISR—the
raw computed BMI value, which was included in the dataset in 2013. In 2014 it was
determined that a truncated BMI was not useful in calculating bmicat_ISR, and
bmi1_ISR was removed from the dataset.
METHOD OF CALCULATION:
COMPUTE bmicat_ISR=0.
IF bmi_ISR >= 10 AND bmi_ISR < 18.5 bmicat_ISR=1
IF bmi_ISR >= 18.5 AND bmi_ISR < 25 bmicat_ISR=2
IF bmi_ISR >= 25 AND bmi_ISR < 30 bmicat_ISR=3
IF bmi_ISR >= 30 AND bmi_ISR < 98 bmicat_ISR=4
IF bmi_ISR = 98 OR bmi_ISR=99 OR rh1 = 1 bmicat_ISR=0
Rapid Risk Factor Surveillance System (RRFSS)
Body Mass Index (BMI)
MODULE INDICATORS
OVERWEIGHT OR OBESE
INDICATOR DESCRIPTION:
% of adults (18+) whose self-reported Body Mass Index (BMI) is 25 or higher
INDICATOR OBJECTIVES:
To measure the proportion of the adult population who is overweight or obese
ANALYSIS CHECK LIST:
Exclude respondents with missing BMI (pregnant, refused, don’t know, height less than 3’
or greater than 6’11” from the denominator)
METHOD OF CALCULATION:
2001-2006 – Need to calculate bmicat_ISR:
Calculate height in metres (hgt_m):
For 2001 & 2002 only:
IF bmi1feet=98 bmi1feet=998.
IF bmi1feet=99 bmi1feet=999.
IF bmi1inch=98 bmi1inch=998.
IF bmi1inch=99 bmi1inch=999.
IF bmi1cent=98 bmi1cent=998.
IF bmi1cent=99 bmi1cent=999.
EXECUTE.
For 2001-2006:
MISSING VALUE bmi1feet (0, 998, 999).
MISSING VALUE bmi1inch (998, 999).
MISSING VALUE bmi1cent (0, 998, 999).
IF SYSMIS(bmi1inch) =1 bmi1inch=0.
COMPUTE hgt_m = (bmi1feet*12 +bmi1inch) *2.54 / 100.
EXECUTE.
IF SYSMIS(hgt_m) =1 hgt_m = bmi1cent / 100.
EXECUTE.
Rapid Risk Factor Surveillance System (RRFSS)
Body Mass Index (BMI)
Calculate weight in kilograms (wgt_kg):
MISSING VALUE bmi2lbs (0, 998, 999).
COMPUTE wgt_kg = (bmi2lbs * 0.4536).
IF SYSMIS(wgt_kg) =1 wgt_kg = bmi2kilo.
EXECUTE.
Calculate body mass index (bmi) (exclude pregnant or height less than 3’ or height
greater than 6’11”)
COMPUTE bmi=0.
IF (rh1 >1 OR SYSMIS(rh1) = 1) AND (hgt_m>=0.91 AND hgt_m <= 2.11) bmi =
wgt_kg/(hgt_m * hgt_m).
EXECUTE.
Calculate bmi categories (bmicat_ISR)
COMPUTE bmicat_ISR=0.
IF bmi_ISR >= 10 AND bmi_ISR < 18.5 bmicat_ISR=1.
IF bmi_ISR >= 18.5 AND bmi_ISR < 25 bmicat_ISR=2.
IF bmi_ISR >= 25 AND bmi_ISR < 30 bmicat_ISR=3.
IF bmi_ISR >= 30 AND bmi_ISR < 98 bmicat_ISR=4.
EXECUTE.
For all years:
% Overweight or Obese
# adults (18+) with BMI >=25 (bmicat_ISR=3 OR bmicat_ISR=4)
# adults (18+) with calculated BMI (bmicat_ISR>0)
Rapid Risk Factor Surveillance System (RRFSS)
*100