A scatter diagram that plots two variables X(hortizontal axis) and Y ( vertical axis)
plotted a single data
the closer point lie with respect to the straight line of best fit through them (called the REGRESSION LINE)
THE STRONGER THE ASSOCIATION BETWEEN THE VARIABLE X AND VARIABLE Y.
100
What is Operationlization ??
the process of defining measurement procedures for the variables used in a study.
Ex. in the study between tobacco use and lung disease, the variables might be the number of cigarettes smoked and the occurrence of asthma.
100
Defining the Role of Chance in Association
Epidemiology use statistical procedure to assess the degree to which chance may have accounted for observed association.
100
What are the two categories of Analytic Studies? Explain them!
Observational Design: investigator
does not have control over the expose factor
Usually is unable to assign subjects randomly to study conditions.
Experimental Design: investigator
Controls who is exposed to a factor of interest
Assign subjects randomly to study groups
100
What is an ODD RATIO (OR) ?
Think about the FOURFOLD TABLE: CASE-CONTROL STUDY
Analyze it!~
Odds Ratio: Is a measure of how many times you see the association between frequency of exposure and frequency of outcome used in case control studies.
Ex: YES (Cases) No (control)
YES A B
NO C D
A+C B+D
odds: A/C B/D
Odds Ration: AD/BC
200
Examples of scatter plot X vs. Y
- perfect direct linear association
-perfect invere linear assocation
-no association
-positive association (e.g., r=0.7)
-curvilinear- (inverted U-shaped)
200
able to assert that a causal association exist between an exposure factor and disease in the host
1. example, is there a causal relationship between smoking and lung cancer?
several criteria of causality must be satisfied before asserting that a causal association exist.
Explain the Causality in epidemiological studies. How is this important.
200
Sample Versus Population? When is it accurate?
Sample based relation give answer to what happen to the entire population
Sample--a subset of the population
A goal of inference is to draw conclusion about a parent population from sample-based data.
As sample size goes up, the probability that the results are due to chance decrease.
Sample size is accurate when the sample clearly match to the population size (gender, age, ect) and clearly represents
200
Why is Ecological studies important?
Studies populations or groups rather than individuals
(ex. nations, states, census, tracts and countries)
May be used when individual m,measurements are not available, but group-level data can be obtained.
200
Meaning of ODD RATIO (CONTINUE)
YES Case-9 Control- 4
NO 95 88
the odds in favor of exposure among the disease group (the cases)= A/C or 9/95
The odds in favor of exposure among the non-disease group (the controls)= B/D or 4/88
The Odd Ration is defined as ( 9/95 and 4/88 or 9*88 and 4*94 divided= 2.08)
300
Name more concepts of Association. Explain them.
Dose-Response Curve-- a type of association between association and an effect (ex. dose-response relationship between cigarettes smoked daily and mortality from lung cancer)
Multimodal Curve--Has several peaks at the frequency of cases ( Ex. changes in lifestyle and immune status of the host
Epidemic Curve--a graphic plotting of the distribution cases by time of the onset. (AIDs in identifying the cause of a disease outbreak)
300
There are 8 criteria of causality. What are they? Explain?
Strength: strong associations give support to a causal relationship between factor and disease
Consistency: An association has been observed repeatedly
Specificity: Association is the constrained to a particular disease-exposure relationship
Temporality: The cause must be observed before the affect
Biological gradient: also known as a dose-response curve; shows a trend in the association between exposure and disease
300
What is Point Estimate?
The value for the population is referred to as a parameter and the corresponding value for the sample is a statistic.
Point estimate is a single value (sample-based) chosen to represent the population parameter.
300
What is Ecological Fallacy?
an erroneous inference that may occur because an association observed between variables on an aggregate level does not represent or reflect the association that exist at an individual level .
Example_ Coronary heart disease
300
How would you Interpret an ODDS RATIO?
1. ODD RAtio > 1 means that there is a positive association between exposure and disease
2. ODD Ratio of 2.1 (2.0) means that the ODDS of exposure are about 2 times higher among the diseased (case) than among the non-diseased (controls)
3. an ODDS RAtion of <1 means that the exposure might be a protective factor (what does protective factor mean)
4. ODDS Ration = 1.0 means NO association between exposure and outcome (not statistically significant)
400
What is a Contingency Table?
It is another method for demonstrating associations
a type of table that tabulates data according to 2 dimensions
--- column and row totals are know as marginal totals
A- exposure is present & disease is present
B- exposure is present & disease is absent
C- exposure is absent and disease is present
D- Exposure is absent and disease is absent
400
Analogy: Related tot he correspondence between associstion and one that being evaluated for causality
Plausibility- the association must be biologically plausible from the standpoint of contemporary biological knowledge.
Coherence- The cause-and-effect- interpretation of the data should not seriously conflict with the generally known facts of the natural history and the biology of the disease.
There are 8 criteria of causality. What are they? Explain?
400
what is Confidence Interval Estimate?
A range of values that with a certain degree of probability contain the population parameter.
Used as an alternative to point estimate.
400
What are the advantages and disadvantages of Ecologic Studies?
**Advantages:
Provide information about the context of health
Can be performed when individual-level measurements are not available.
Can be conducted rapidly and with minimal resources
**Disadvantages:
Ecologic fallacy
Imprecise measurement of exposure
400
Why do we use the Case-Control Studies ? What are the advantages and disadvantages?
Advantages:
1. Can be used to study low-prevalence conditions
***Having a disease is a criterion for being selected as a case
3. Relatively quick and easy to complete
4. Usually inexpensive
4. Involve smaller number of subjects
Disadvantages:
1. Measurement of exposure may be inaccurate
2. Representatives of the cases and controls may be unknown
3. Provide indirect estimates of risk
4. When the person becomes exposed to the disease, the outcome cannot always be certain
500
What is an Epidemiology Research strategies ?
Epidemiologist ask whether a particular exposure is causally associated with a given outcome.
Investigators:
1. examine existing facts and hypothesis
2. Formulate a new or more specific hypothesis
3. Obtain additional facts to test the acceptability of the new hypothesis
500
What are causal factors?
Many types of causal relationship involve more than one causal factor.
Multiple causal factors can include:
specific exposures (e.g smoking)
family history (genetics)
lifestyles characteristics
Environmental influences
500
What is Power?
Power tells us the probability
Power is the ability of a study to demonstrate an association if one exist.
Related to sample size and effect size
Effect size is related to the strength of the association that has been observed.
500
What are CASE CONTROL STUDIES? WHAT IS IT USED FOR/ HOW IS IT USED?
Design to study ware conditions
Subjects are defined on the basic of the presence or absence of an OUTCOME of interest
**Cases are individual WHO HAVE the OUTCOME or disease of interest
**CONTROLS Do not have the outcome or disease of interest.
500
Define Cohort Studies? why is it Important?
A cohort study is a population group, or subset thereof, (distinguished by a common characteristic) that is followed over a period of time. This studies exposures factors.
Example:
Birth or age cohort
work cohort