WEEK 4: RANDOM SAMPLING ERROR, BIAS Flashcards
What is the goal of epidemiology and health research
Identification of causes and preventions for disease
Strong evidence is:
1) Of the lowest possible random sampling error (a
statistically significant exposure/outcome association)
2) Based on a good design
➢ Free of selection and information biases
➢ Under minimal influence of confounding (next
session)
Sources of Error
- chance
- bias
- systematic error in selection of partipants and or measurement - cofounding
Bias
- refers to a systematic error in the design or conduct of a study
- When bias occurs in a study the observed association between the exposure
and outcome will be different from the true association
two types of biases
selection bias, information bias
consequence of information bias
people will be classified into a wrong
cell (recall the 2X2 table): misclassification
Selection Bias
refers to a systematic error in the way participants are
selected or retained in a study
- when individuals have different probabilities of being included or retained in the study according to the exposure and/or
outcome.
Why does selection bias happen
➢How we approach people, how we invite them, whether
they decide to be part of (or remain in) the study….
➢Not issues related to sampling (random sampling error,
generalizability)
Types of Selection bias
- Inappropriate control selection (case control)
- Differential Participation ( case control, cohort)
- Diffrential loss to follow up (cohort, expiremental)
Examples of selection bias
volunteer bias, non response bias, membership bias, loss to follow up bias
reducing selection bias
➢Little (or nothing) can be done to fix selection bias once it has occurred
- must be avoided in design and conduct
Information bias
Can occur when the means for obtaining info about the subjects in the study arte flawed so that some of the info gathered regarding exposures and diseases outcomes is incorre
Recall Bias
operates to enhance recall in cases compared with controls
- Certain pierce of info (potentially relevant exposure) may be recalled by case but forgotten bya control
Reporting Bias
a subject may be reluctant to report an exposure he is aware of bc of attitudes, beliefs, and perceptions
Wish Bias
introduced by subjects who have developed a diseases and who, in attempt to answer the question” “Why me”, seek to show that the disease is not their fault
Internal Validity
inner workings of a study
- can not be measured or quantified
external validity
refers to how well the results of this particular study could be applied to the larger population
Healthy Worker Bias
type of selection bias referring to the fact that people who can work are generally healthier than the overall population bc the overall population includes people who are too sick to work
sensitivity analysis
set of extra analyses conducted after the main results of a study are known with the goal of quantifying how much bias there might have been and in which direction it shifted the results
confidence interval
explicit admission that the result of a study (the point or effect estimate) is not exactly right, but the real answer is somewhere within a given range - the confidence interval
- if we repeat the study many times with different people, 95% of the 95% CI would include the true value
statistical vs clinical significance
the clinical significance observes dissimilarity between the two groups or the two treatment modalities, while statistical significance implies whether there is any mathematical significance to the carried analysis of the results or not
