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RUSVM Epidemiology > Measure Of Association And Bias/Confounding > Flashcards

Measure Of Association And Bias/Confounding Flashcards

1
Q

Measures of association are used in what types of studies?

A

Analytical studies

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2
Q

If there is the same amount of disease in both exposed and non-exposed group, that means the out come is (associated or non-associated)

A

Non- associated

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3
Q

What type of measure of association can we use in cross-sectional and case-control studies?

A

Odds ratio

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4
Q

What types of measure of association can be used in prospective cohort or clinical trials?

A 
Relative risk (incidence)
Attributable risk
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5
Q

What type of measure of association can be used in retrospective cohort and cross-sectional studies?

A

Prevelence ratio

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6
Q

What is the odds ratio?

A

= odds of exposure in diseased animals / odds of exposure in non-diseased animals

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7
Q

If the odds ratio = 1, what does this mean?

A

Exposure is the same between diseased and non-diseased => no association

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8
Q

If the odds ratio is > 1, what does this mean?

A

Exposure among diseased is greater than control => positive association

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9
Q

If odds ratio is < 1, what does this mean?

A

Exposure among diseased is less than control => negative association

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10
Q

What is relative risk?

A

Compares risk of exposure and non-exposed groups

RR= (risk in exposed group) / (risk in un-exposed group) 
RR= [a/(a+b)] / [c/(c+d)]
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11
Q

What is the amount/proportion of overall disease incidence in a population or group that can be attributed to a specific exposure?

A

Attributable risk

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12
Q

What is the difference between AR due to etiologic fraction and AR in the population

A

AR (etiologic)- how much disease is attributed to factor in study

AR (population) - how much disease in target population is attributed to factor in study

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13
Q

What is a measure used to compared the amount of disease that has occurred in the exposed and un-exposed population in retrospective studies?

A

Prevelence

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14
Q

Case control uses what measure of association ?

A

Odds ratio

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15
Q

Prospective cohorts uses what measure of association?

A

Relative risk

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16
Q

Retrospective cohorts uses what measure of association ?

A

Prevelence rate

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17
Q

Clinical trials use what measures of association?

A

Relative risk

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18
Q

__________ relates to the absence of systemic error in a study result

A

Validity

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19
Q

_______________ is the extent to which a measure of association from a study differs from the true measure of association in the source population

A

Bias

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20
Q

What does it mean for a study to have internal validity?

A

The study result is valid with respect to population under study

21
Q

What does it mean for a study to have external validity?

A

The study result is valid to a wider population beyond the study and source population

22
Q

What are sources of bias?

A

Selection bias -> error in selection of study subjects (sample is different from population)

Informational (misclassification) bias -> error in measurement

23
Q

What is an unknown factor that will disrobed the relationship between he exposure and outcome?

A

Confounding

24
Q

How can bias be reduced in a cross-sectional descriptive study?

A

Random sampling (a biased sample would have more or less disease than the true population)

25
Q

How can bias be reduced in case-control studies?

A

Match controls with demographics, age, and breed

26
Q

How can bias be reduced in a cohort study?

A

Matching to ensure exposed and non exposed have similar demographics

27
Q

What are 3 types of selection bias?

A

Self selection bias -> based on volunteers
Healthy worker bias-> those working are in better health than pop
Diagnostic bias-> diagnosis influenced by vets knowledge, exposure, and expectations

28
Q

An error is considered ______ if it is not related t the exposure or the disese

A

Non-differential

29
Q

If a error in measurement is related to the exposure or outcome it is ____________

A

Differential

30
Q

How can information bias be reduced?

A

Evaluation of accuracy of measuring tools

31
Q

What are types of information bias?

A

Observer variation (interpretation)
Deficiency of tools and technical errors
Recall bias
Reporting bias

32
Q

T/F: confounders influence both exposure and outcome by distorting measure of association.

A

True

33
Q

What are the 3 conditions for a confounder?

A

Associated with exposure
Associated with outcome
Not in the causal pathway between exposure and outcome

34
Q

If you realize there may be a condfounding factor affecting a study you already preformed, how can you reduce this effect?

A

Stratify data -> parturition results based on the confounding factor

35
Q

Prior to a study how can confounding factors be reduced?

A

Match the study so confounder is equally represented in both groups

Restriction - do not enroll individual with confounding factor

Randomization

36
Q

What type of error in a study is due to chance

A

Random error - fluctuations around a true value because of sampling or measuring

37
Q

What type of error is due to bias?

A

Systematic error - error that is inherent to the study method being used -> results are skewed in a predictable and repeatable error

38
Q

Random variation in a study is measured by what two tests?

A

Confidence interval -> range of values in which true value is found

P-value -> statistically significant

39
Q

A large confidence interval will mean what about the sample size

A

Small sample size

40
Q

T/F: if the 95% confidence interval for the odds ratio includes 1, the odds ratio is statistically significant?

A

FALSE

If the 95% confidence interval for the odds ratio DOES NOT include 1, it is statistically significant

41
Q

Odds ratio > 1
Confidence interval includes 1
Is there an association?

A

No association, not statistically significant

42
Q

Odds ratio <1
Confidence interval does not include 1
Is there an association?

A

Negative association

Statistically significant

43
Q

A P-value is statistically significant if it is _______

A

<0.05

44
Q

What is a null hypothesis?

A

Statement saying there is no association. (We want to reject the null hypotheses)

45
Q

What are the types of error in statistical significance?

A

Type 1 (a) - False positive (reject null when it is NOT false)

Type II (B)- False negative (accept the null when it is FALSE)

46
Q

If the explanatory and outcome variables are both categorical, what type of central tendency test do you use?

A

Chi-squared (for all two by two tables)

47
Q

If the explanatory variable is categorical and the outcome variable is continuous, what test do you use for central tendency?

A

Students t test

48
Q

If the explanatory and outcome variables are both continuous, what measure of central tendency is used?

A

Correlation

RUSVM Epidemiology (14 decks)

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