Biostat

Question 1

Case-Control Study

Answer 1

Compare a group of people WITH disease to a group WITHOUT disease, looking for PRIOR exposure or risk factor. “What happened?”

Question 2

Cohort Study

Answer 2

Compares a group WITH a given exposure or risk factor to a group WITHOUT such exposure, looking to see if an exposure INCREASED the likelihood of disease. “Who will develop disease?” or “Who developed the disease?”

Question 3

Cross-sectional Study

Answer 3

Collects data from a group of people to assess the FREQUENCY of disease and related risk factors at a particular point in time. “What is happening?”

Question 4

Phase I clinical trial

Answer 4

Small number of HEALTHY volunteers - assess safety, toxicity, and pharmacokinetics

Question 5

Phase II clinical trial

Answer 5

Small number of patients WITH DISEASE OF INTEREST - assess treatment efficacy, optimal dosing, and adverse effects

Question 6

Phase III clinical trial

Answer 6

LARGE number of patients randomly assigned either to the treatment under investigation or to the best available treatment or placebo - COMPARES the new treatment to current standards

Question 7

Phase IV clinical trial

Answer 7

POSTMARKETING SURVEILLANCE trial of patients after approval - detects rare or long-term adverse effects

Question 8

How does PPV vary with prevalence

Answer 8

It varies directly with prevalence or pretest probability i.e. high pretest probability –> high ppv

Question 9

How does NPV vary with prevalence

Answer 9

It varies inversely with prevalence or pretest probability i.e. high pretest probability –> low NPV

Question 10

Odds ratio

Answer 10

Odds that the group with the disease (CASES) was exposed to a risk factor divided by the odds that the group without the disease (CONTROLS) was exposed; used in case-control studies

Question 11

Relative Risk

Answer 11

Risk of developing disease in the exposed group divided by risk in the unexposed group; used in cohort studies

Question 12

RR = 1 indicates what?

Answer 12

That risk of developing disease is the same in exposed and unexposed individuals

Question 13

Attributable Risk

Answer 13

Difference in risk between exposed and unexposed groups, or the proportion of disease occurrences that are attributable to the exposure

Question 14

Absolute Risk Reduction

Answer 14

Absolute reduction in risk associated with a treatment as compared to a control

Question 15

Number needed to treat

Answer 15

Number of patients who need to be treated for 1 patient to benefit. 1/absolute risk reduction

Question 16

Number needed to harm

Answer 16

Number of patients who need to be exposed to a risk factor for 1 patient to be harmed. 1/attributable risk

Question 17

Effect modification

Answer 17

The effect of the main exposure on the outcome is modified by the presence of another variable

Question 18

Selection bias

Answer 18

Nonrandom assignment to participation in a study group

Question 19

Recall bias

Answer 19

Knowledge of presence of disorder alters recall subjects; common in retrospective studies

Question 20

Sampling bias

Answer 20

Subjects not representative of general population; type of selection bias

Question 21

Late-look bias

Answer 21

Information gathered at an inappropriate time i.e. using a survey to study a fatal disease - only patients still alive can answer

Question 22

Procedure bias

Answer 22

Subjects in different groups are not treated the same

Question 23

Confounding bias

Answer 23

Occurs when factor is related to both exposure and outcome, but is not on the causal pathway

Question 24

Lead-time bias

Answer 24

Early detection confuse with increased survival

Question 25

Observer-expectancy effect

Answer 25

Occurs when a researcher’s belief in the efficacy of the Tx changes the outcome of that Tx

Question 26

Hawthorne effect

Answer 26

Occurs when the group being studied changes its behaviors owing to the knowledge of being studied

Question 27

Null hypothesis

Answer 27

Hypothesis of no difference

Question 28

Alternative hypothesis (H1)

Answer 28

Hypothesis of some difference

Question 29

Type 1 error (alpha)

Answer 29

Stating that there IS an effect/diffference when NONE exits (mistakenly accept the alternative and reject the null); aka false-positive error

Question 30

Type 2 error (beta)

Answer 30

Stating that there IS NOT an effect/difference when ONE EXISTS (failure to reject the null); aka false-negative error

Question 31

Z score of 95% CI

Answer 31

1.96

Question 32

Z score of 99% CI

Answer 32

2.58

Question 33

T-test

Answer 33

Checks difference between the MEANS of 2 groups

Question 34

ANOVA

Answer 34

Checks difference between the means of 3 or more groups

Question 35

Chi square

Answer 35

Test checks difference between 2 or more PERCENTAGES OR PROPORTIONS of categorical outcomes

Question 36

Crossover study

Answer 36

Subjects are randomly allocated to a sequence of 2 or more treatments given consecutively; a washout period is often added between treatment intervals to limit confounding effects of prior treatment

Question 37

Case series

Answer 37

Descriptive study that tracks patients with known condition to document natural history or response to treatment; qualifying study that does not quantify statical significance