Measure Of Association And Bias/Confounding

Question 1

Measures of association are used in what types of studies?

Answer 1

Analytical studies

Question 2

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)

Answer 2

Non- associated

Question 3

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

Answer 3

Odds ratio

Question 4

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

Answer 4

Relative risk (incidence)
Attributable risk

Question 5

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

Answer 5

Prevelence ratio

Question 6

What is the odds ratio?

Answer 6

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

Question 7

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

Answer 7

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

Question 8

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

Answer 8

Exposure among diseased is greater than control => positive association

Question 9

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

Answer 9

Exposure among diseased is less than control => negative association

Question 10

What is relative risk?

Answer 10

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)]

Question 11

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

Answer 11

Attributable risk

Question 12

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

Answer 12

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

Question 13

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

Answer 13

Prevelence

Question 14

Case control uses what measure of association ?

Answer 14

Odds ratio

Question 15

Prospective cohorts uses what measure of association?

Answer 15

Relative risk

Question 16

Retrospective cohorts uses what measure of association ?

Answer 16

Prevelence rate

Question 17

Clinical trials use what measures of association?

Answer 17

Relative risk

Question 18

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

Answer 18

Validity

Question 19

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

Answer 19

Bias

Question 20

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

Answer 20

The study result is valid with respect to population under study

Question 21

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

Answer 21

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

Question 22

What are sources of bias?

Answer 22

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

Informational (misclassification) bias -> error in measurement

Question 23

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

Answer 23

Confounding

Question 24

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

Answer 24

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

Question 25

How can bias be reduced in case-control studies?

Answer 25

Match controls with demographics, age, and breed

Question 26

How can bias be reduced in a cohort study?

Answer 26

Matching to ensure exposed and non exposed have similar demographics

Question 27

What are 3 types of selection bias?

Answer 27

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

Question 28

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

Answer 28

Non-differential

Question 29

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

Answer 29

Differential

Question 30

How can information bias be reduced?

Answer 30

Evaluation of accuracy of measuring tools

Question 31

What are types of information bias?

Answer 31

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

Question 32

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

Answer 32

True

Question 33

What are the 3 conditions for a confounder?

Answer 33

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

Question 34

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

Answer 34

Stratify data -> parturition results based on the confounding factor

Question 35

Prior to a study how can confounding factors be reduced?

Answer 35

Match the study so confounder is equally represented in both groups Restriction - do not enroll individual with confounding factor Randomization

Question 36

What type of error in a study is due to chance

Answer 36

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

Question 37

What type of error is due to bias?

Answer 37

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

Question 38

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

Answer 38

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

Question 39

A large confidence interval will mean what about the sample size

Answer 39

Small sample size

Question 40

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

Answer 40

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

Question 41

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

Answer 41

No association, not statistically significant

Question 42

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

Answer 42

Negative association | Statistically significant

Question 43

A P-value is statistically significant if it is _______

Answer 43

<0.05

Question 44

What is a null hypothesis?

Answer 44

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

Question 45

What are the types of error in statistical significance?

Answer 45

Type 1 (a) - False positive (reject null when it is NOT false) Type II (B)- False negative (accept the null when it is FALSE)

Question 46

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

Answer 46

Chi-squared (for all two by two tables)

Question 47

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

Answer 47

Students t test

Question 48

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

Answer 48

Correlation