به نام ايزد يكتا دكتر داودخليلي. cut points of obesity dr. khalili phd...
TRANSCRIPT
به نام ايزد يكتا
دكتر داودخليلي
Cut points of
OBESITY
Dr. KhaliliPhD candidate in epidemiologyShahid beheshti university (MC)
Some Points About Dichotomizing continuous predictors
Simplicity & Practicality Measurement error & low PowerTrade off
Avoid of assumptions
Calculate better effect measurements
We loss some information
Throwing about 1/3 of data away
Some Points About Dichotomizing continuous predictors
Dichotomizing
According to variable distribution
Using a gold standard (usually another variable or event )
Dichotomizing: to create two relatively homogenous group
85% or …of percentile
Cut points based on a Gold Standard
Receiver Operating Characteristic Curve (ROC)
AUC (area Under the Curve)
Sensitivity 1
1 - specificity
Cut points based on a Gold Standard (ROC)
Sensitivity + Specificity -1
Min
Max
Calculating an effect measure (OR, RR, HR, …)
To compare with a reference
Agreement Chart
Cut points based on a Gold Standard
National Health and NutritionExamination Surveys
NHES I 1960-6218-79 years
NHES II 1963-656-11 years
NHES III 1966-7012-17 years
NHANES I 1971-751-74 years
NHANES II 1976-806 mo.-74 years
HHANES 1982-84 6 mo.-74 years
NHANES III 1988-942 mo. +
NHANES 1999-All ages
Survey Dates Ages
OP96025
NIH consensus conference (1985):
·According to NHANES II and 85th percentile values
(men and women ages 20-29 y)
·BMI of 27.8 for men
·BMI of 27.3 for women
05
10152025303540
Men 20-74 y Women 20-74 y
1960-62 1971-74 1976-801988-94 1999-2000
Probloms of this statistical approach:Distribution Changes
Theoretical Curves
Need of more information on BMI complication
Low sensitivity because of underestimation of Obesity
Age-adjusted trends in obesity (BMI >=30): United States
1995 WHO expert committee report
For adults, the Expert Committee
proposed classification of BMI with the
cut-off points 25, 30 and 40…This
classification is based principally on
the association between BMI and
mortality.
BMI cut-points of 25 (overweight) and 30 (obesity) recommended by expert committees
Relation between mortality and BMI
Data from Lew EA: Mortality and weight: insured lives and the American Cancer Society studies. Ann Intern Med 103:1024-1029, 1985.
The method used to establish BMI cut-off
points has been largely arbitrary. In
essence, it has been based on visual
inspection of the relationship between
BMI and mortality: the cut-off of 30 is
based on the point of flexion of the
curve.
1998 NHLBI (National Heart, Lung, and Blood Institute )
Clinical Guidelines
In this report, overweight is defined as a BMI of 25.0 to 29.9
kg/m2 and obesity as a BMI of 30 kg/m2. The rationale
behind these definitions is based on epidemiological data
that show increases in mortality with BMIs above 25
kg/m2. The increase in mortality, however, tends to be
modest until a BMI of 30 kg/m2 is reached.
BMI is in itself a strong predictor of overall mortality both above and below the apparent
optimum of about 22·5–25 kg/m2. The progressive excess mortality above this range is
due mainly to vascular disease and is probably largely causal. At 30–35 kg/m2, median
survival is reduced by 2–4 years; at 40–45 kg/m2, it is reduced by 8–10 years (which is
comparable with the effects of smoking). The definite excess mortality below22· 5 kg/m2 is
due mainly to smoking-related diseases, and is not fully explained.
Recent study in western Europe and North America
“Body-mass index and cause-specific mortality in 900 000 adults:collaborative analyses of 57 prospective studies”
Lancet. 2009 March 28; 373(9669): 1083–1096.
Ischaemic heart disease and stroke mortality versus BMI in the range 15–50 kg/m2
Lancet. 2009 March 28; 373(9669): 1083–1096.
Because of some Reasons:WC instead of BMI
WC cut points
According to:
- Lean MEJ, Han TS, Morrison CE. Waist circumference as a measure for indicating need for weight management. BMJ 1995;311:158–61.
Randomly recruited 904 men and 1014 women,aged 25 to 74 years, from the general population ofnorth Glasgow between January and August 1992,excluding only those who were chair bound.
BMI asGold Standard
Using in ATPIII & EGIR
T S Han, EMvan Leer, J C Seidell, ME J LeanWaist circumference action levels in the identification of cardiovascular risk factors: prevalence study in a random sample. BMJ, 1995;311:1401-5
These cutpoints have been shown, in a random sample of 2183 men and 2698 women from the Netherlands, to be associated crosssectionally with an adverse cardiovascular risk profile.
T S Han, EMvan Leer, J C Seidell, ME J Lean1995;311:1401-5
BMI 25 at action level I or 30 at action level 2as Gold standard
T S Han, EMvan Leer, J C Seidell, ME J Lean1995;311:1401-5
ShanKuan Zhu,Am J Clin Nutr 2002;76:743–9.
Current WC cutoffs proposed by the National Institutes ofHealth and the World Health Organization were not chosen on thebasis of their empirical relation to risk factors. Rather, these cutoffswere derived by identifying WC values corresponding to BMIcutoffs for overweight (BMI = 25) or obesity (BMI = 30) (2, 21_).
If WC has an independent or a stronger association with risk factors
than BMI has, then it is inappropriate to base WC thresholdson their association with BMI thresholds. Rather, thresholds foreach should be based on their relation to risk factors. Hence, existingcutoff recommendations may not take full advantage of therelation between WC and obesity-related cardiovascular diseaserisk factors.
WC cutoffs among Chinese adults
Country/ethnic-specific values for WC A Consensus Statement from the IDF
Diabet. Med. 23, 469–480 (2006)
Cohort Studies to determine WC cutoff
Brazil HTN ----- M:87 F:80
2009
Australia CVD mortality 20-69 M:96 F:80
2007
Japan CVD ≥ 40 M:90 F:80
2009
Thailand CHD 35-59 M:82
2007
China* CVD risk 18-93 M:83-88 F:76
2007
Iran CVD ≥ 40 M:94.5 F:94.5
2009
Country Outcome Age Cut off P.Y.
Different Gold Standard
Different Cut points
The more Hard Outcome with lower prevalence
The higher Cut pointOne prevalent CVD rick factorTwo prevalent CVD rick factorThree prevalent CVD rick factorIncident CVDCVD mortality
پس است ديگری شروع پايان، هربازهم
به نام ايزدمان