真实性与偏倚

Bias & Validity
in Epidemiological Research 流行病学研究中的偏倚与真实性
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Main contents
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3Should I believe the results?Coffee Diabetes
Chance?Confounding?Bias?
True association
Causal
Non-causal
Measurement Error
Random error
Systematic error
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Measurement error: Implications for epidemiologic studies
Measurement error in the exposure or the outcome RANDOM ERROR
Systematic error
Measurement error in a confounder
Random error
Systematic error
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Measurement error: Implications for epidemiologic studies RANDOM ERROR
Systematic error
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8Attenuation of the relations 随机误差减弱关联强度
P h y s i o l o g i c a l v a r i a b l e s *
****
***
R=0.96R=0.65
Random error 随机误差
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Random error can be problematic,
but . . .
–increasing sample size
–changing design
–improving instrumentation
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How do we quantify random error in
a test or a study?
–Coefficient of variation, CV
–Repeat measures, CV = SD/mean
–Hypothesis testing, p-value, 95%CI
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Bias
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Definition of bias
Bias is systematic,non-random
processes leading
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Question?
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Errors in epidemiological studies
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Classification of bias 分类
•Selection bias
•Information bias
•Confounding bias
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SELECTION BIAS -definition
SELECTION BIAS选择偏倚:
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Sampling and representativeness
Sample
Target Population
Sampling
Population Target Population →Sampling Population →Sample
选择性偏倚的来源
1. Sampling bias 抽样偏倚--
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选择性偏倚的来源
2. Participation bias 参加者偏倚
–Self-selection
–Non-response
–Healthy worker effect
–Differential loss to follow-up
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选择性偏倚的来源
3. Ascertainment bias 确认偏倚--
–Prevalence-incidence bias
–Referral bias
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选择性偏倚的来源
3. Ascertainment bias 确认偏倚
–Diagnostic bias
–Admission rate bias
–Lead time bias
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Sampling bias 抽样偏倚
Cases
liver cirrhosis
Controls A trauma ward
Heavy alcohol use 80 40
Light/no alcohol use 20 60
OR=6
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Sampling
bias 抽样偏倚
Cases liver cirrhosis
Controls A
trauma ward
Controls B
non-trauma
Heavy alcohol use 80 40 10 Light/no alcohol use 20 60 90
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Diagnostic bias 诊断偏倚
Cases
Controls
uterine cancer
Takes oral
a b
contraceptives
Does not take oral
c d
contraceptives
•
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26Non-response bias 无应答偏倚
Papanicolau test Cases of
cervical cancer Controls
Did not have test a b Had test c d Total 1000 1060
••Paper smear Had test Didn’t have test
Healthy worker effect
健康工人效应
Exposed workers
General population
Deaths 50 7,000
Person-time
in years
1,000 100,000
Mortality (cases/year) 0.05 0.07
RR=0.7
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Healthy worker effect
General
population
Exposed workers Workers
Non-
workers
Total
Deaths 50 4,500 2,500 7,000 Person-
time
1,000 90,000 10,000 100,000
Mortality
(cases/yr)
0.05 0.05 0.25 0.07
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Admission bias
HCV与肝癌的meta分析结果
病例-对照来源研究数目OR (95%CI)
医院—医院87.80 (5.04—12.06)
医院—社区7 6.70 (3.28—13.68)
社区—社区9 3.34 (2.44—4.56)
（吴江南等. 中华肝脏病杂志2007）
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Loss to follow-up bias
失访偏倚
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Quick Quiz
To assess the association of exercise and CHD in a cohort study
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Quiz Answer
If the no-phone subjects differ only
CHD death, then this would
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Answer continued. . .
both
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Information bias
信息偏倚
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Information bias
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Sources of Information bias
偏倚的来源•Respondent
•Data collector
•Instrument
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Sources of information bias •Data managers
•Data analysts
•Data interpreters :
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Main types of information bias
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Definition of common information Bias-1•Data collection bias
•Recall bias
•Detection bias
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Definition of common information Bias-1•Interviewer bias
•Reporting bias
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exposures better than mothers with healthy children
Recall bias 回忆偏倚
Mothers of
Children with malformation
Controls
Took tobacco,alcohol, drugs a
b
Did not take
c d
Cases remember exposure differently than controls
•Overestimation of “a” overestimation of OR
Recall bias 回忆偏倚
子女患风湿性关节炎与父母患病关联的病例对照研究
风湿性关节炎风湿性关节炎
父母风湿性关节炎子女病例普通对照OR
子女病例
同胞对照OR
无
3111 1.01120 1.0一方1074 5.02317 2.5双方61613.963 3.6（Schull and Cobb, 1969）
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Interviewer bias 访问者偏倚Investigator asks cases and controls differently about exposure
Cases of
Controls
listeriosis
Eats soft cheese a b
Does not eat
c d
soft cheese
•Overestimation of “a” overestimation of OR
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Biased follow-up偏性随访Unexposed are less diagnosed for disease than exposed
•Example
-Cohort study to investigate risk factors for
mesothelioma间皮瘤
-Difficult histological diagnosis
-Histologist more likely to diagnose specimen
as mesothelioma if asbestos(石棉) exposure
kown
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Impact of information bias:
Misclassification Measurement error leads to assigning wrong exposure or
outcome category
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Impact of information bias:
Misclassification
•Non-differential 无差异错误分类（错分）
Measure of effect tends toward 1•Differential 差异错分
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60404060D
E ¯E
D ¯OR = 60*60/40*40 = 2.25
100
100
48325268D E ¯E
D ¯100
100
Percent Exposure Misclassification:
20% 20%
OR = 48*64/36*52 = 1.96
OR
Differential misclassification
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Differential misclassification
60404060D
E ¯E
D ¯OR = 60*60/40*40 = 2.25
100
100
57324368D E ¯E
D ¯100
100
Percent Exposure Misclassification:
5% 20%
OR = 48*64/36*52 = 2.74。