Chapter 2

Question 1

Validity

Answer 1

does the test accurately id whether a pt has a disease?

• gold standard test
• 2x2 table format

Question 2

Sensitivity

Answer 2

probability that a person with disease has a positive test

- the true positive rate

Question 3

Specificity

Answer 3

probability that a non-diseased person has a negative test

- the true negative rate

Question 4

Positive Predictive Value

Answer 4

probability that a person w/ a + test has disease

Question 5

Negative Predictive Value

Answer 5

probability that a person w/ a - test does not have disease

Question 6

Prevalence of Disease

Answer 6

proportion of pts in the disease present column

Question 7

Likelihood Ratio

Answer 7

probability of obtaining a given test result in a diseased patent divided by the probability of obtaining a given test result in a non-diseased patient
- tells us how much a test result changes the pre-test disease probability (prevalence) to the post-test disease probability

Question 8

higher likelihood ratio for positive test

Answer 8

indicates that a positive test is more likely to be coming from a diseased person than from a non-diseased person, increasing confidence that a person w/ a + result has disease

Question 9

lower likelihood ratio for negative test

Answer 9

negative test is much more likely to be coming from a non-diseased person than from a diseased person, increasing our confidence that a person w/ a - test does not have disease

Question 10

Bayes Theorem

Answer 10

one way to use likelihood ratios to revise probabilities for disease

Question 11

Ways to use Likelihood Ratios

Answer 11

Bayes Theorem
Fagan Nomogram
Natural Frequencies

Question 12

Natural Frequencies

Answer 12

represent the joint frequency of 2 events, such as # of pts w/ disease and the # who have a + test result

Question 13

Kappa Score

Answer 13

(reproducibility)

measures amount of agreement that occurs beyond chance (higher = better)

Question 14

Precision

Answer 14

(reproducibility)

being able to apply the same test to the same unchanged person and obtain the same results

Question 15

coefficient of variation

Answer 15

statistical test used to characterized precision

- the standard deviation divided by the mean value (lower = greater precision)

Question 16

Primary Prevention

Answer 16

interventions designed to prevent disease

Question 17

Secondary Prevention

Answer 17

screening tests designed to find disease or disease processes at an early, asymptomatic stage

Question 18

Evidence Pyramid

Answer 18

1. Systematic Reviews
2. Randomized Control Trials - strongest health promotion recommendations are based on these results
3. Cohort Studies
4. Case-Control Studies
5. Case Series, Case Reports
6. Editorials, Expert Opinion

Question 19

Selection Bias

Answer 19

• occurs when comparison groups have systematic differences in their baseline characteristics what can affect the outcome of the study
• creates problems interpreting observed differences in outcomes n/c they could result from the interventions or the baseline differences between groups
• randomly allocating subjects to the intervention is the best approach to minimize this

Question 20

Performance Bias

Answer 20

• occurs when there are systematic differences in the care received between comparison groups (other than intervention)
• creates problems in interpreting outcome differences
• Minimize by: blinding subjects and providers to the intervention

Question 21

Detection Bias

Answer 21

• Occurs: systematic difference in efforts to diagnoses ot ascertain outcome
• Minimize by: blinding outcomes assessors (ensuring that they are unaware of the intervention received by h\the subject)

Question 22

Attrition Bias

Answer 22

• Occurs: systematic differences in the comparison groups in the number of subjects who do not complete the study
• failing to account for these difference can lead to incorrectly estimating the effectiveness of an intervention
• Minimize by: using an intervention-to-treat analysis, where all analyses consider all subjects who are assigned to a comparison group, regardless of whether they received to completed the intervention

Question 23

statistics used to characterize the performance of a treatment of prevention intervention:

Answer 23

• relative risks
• relative risk difference (reduction or increase, reflecting benefit or harm)
• absolute risk difference (reduction or increase, reflecting benefit or harm)
• numbers needed to treat
• numbers needed to harm

Question 24

Experimental Event Rate

Answer 24

probability that an intervention subject had the outcome

Question 25

Control Event Rate

Answer 25

probability that a control subject had the outcome

Question 26

Relative Risk

Answer 26

probability of an outcome in the intervention group compared to the probability of an outcome in the control group

Question 27

Relative Risk Difference

Answer 27

proportion of baseline risk is reduced/increased by the therapy

Question 28

Absolute Risk Difference

Answer 28

difference in outcome rates between the comparisons groups

Question 29

Reciprocal of the absolute risk difference

Answer 29

number of subjects who need to be treated over a specific period of time to prevent one outcome
- if intervention increases risk of a bad outcome this statistic becomes the number needed to harm

Question 30

guideline recommendations: US Preventative Services Task Force Approach

Answer 30

assigns 1-5 ratings and a level of certainty regarding net benefits

Question 31

guideline recommendations: Grading of Recommendations, Assessment, Development, and Evaluation (GRADE)

Answer 31

rates quality of the evidence and grades the strength of recommendations in clinical guidelines
- primary goals (1) clearly separate quality of evidence and strength of recommendations [A,B,C] (2) provide clear, pragmatic interpretations of strong v. weak recommendations [1,2]