Biostats

Question 1

Incidence

Answer 1

new cases/total population

Question 2

Prevalance

Answer 2

total with disease (new and old) / total population

Question 3

Confidence interval range

Answer 3

Mean +/- (Z x SEM)

90% confidence Z = 1.645
95% confidence Z = 1.96
99% cofidence Z = 2.58

If CI for odds ratio or relative risk crosses 1 - no association between risk and the disease

If CI for study of two treatment groups crosses 0, no actual difference between two treatments

Question 4

Standard deviations

Answer 4

1 SD - 68%
2 SD - 95%
3 SD - 99.7%

Question 5

Case report/ case series

Answer 5

Report of an interesting/ unusual case (or a series of such cases) to describe the common features of the disease

Question 6

Cross-sectional survey

Answer 6

Survey of a large number of people to determine disease prevalence and identify potential risk factors

Question 7

Case control study

Answer 7

Retrospective - compare a group with the disease to group of healthy controls
Identify potential risk factors
Ideal for studying rare diseases
Allows calculation of odds ratio
Subject of late look bias (participants die) and recall bias

Question 8

Cohort study

Answer 8

Follow a cohort that is exposed to a given risk factor to see how many of them developed a particular disease overtime

Usually prospective

Confirms risk factors (or risk reduction) and allows calculation of relative risk

Question 9

Randomized clinical trial

Answer 9

Compares the effect of an intervention in an experimental group to a control group

Subjects are randomized into two groups

Usually double blinded to avoid bias

Question 10

Meta-analysis

Answer 10

Pool the data for multiple studies to create a larger dataset

Can help resolve conflicts in the medical literature

Maybe subject to publication bias

Limited by the quality of the original studies

Question 11

Type one error

Answer 11

Study shows relationship between two phenomena that does not exist

The study findings inappropriately reject null hypothesis (null is true)

Question 12

Type II error

Answer 12

Study fails to show the relationship between two phenomena that does exist

The study fails to appropriately reject the null hypothesis (null is false)

Question 13

Changing behavior that can result from a study group knowing that they are being observed

Answer 13

Hawthorne effect

Question 14

Findings are influenced by the actions of the people collecting or interpreting the data

Answer 14

Investigator bias

Question 15

Information is gathered too late to draw accurate conclusions about the disease or risk factor in the entire intended study population

Answer 15

Late look bias

Question 16

Early detection of a disease increases the time that a person survives after diagnosis, even if the natural history of disease is unchanged

Answer 16

Lead time bias

Question 17

Screening detects slowly progressive cases of the disease and misses rapidly progressing cases

Answer 17

Length bias

Question 18

Study participants drop out of a study and cannot be contacted for follow-up

Answer 18

Loss to follow-up

Question 19

Subjects awareness of being studied alters their reporting of subjective findings; maybe avoided by double blinding and placebo controls

Answer 19

Observation bias

Question 20

Study groups are not treated the same

Answer 20

Procedure bias

Question 21

Studies that show a difference between two groups are more likely to be published in studies that do not show difference

Answer 21

Publication bias

Question 22

Difference and recall between the two study groups

Answer 22

Recall bias

Question 23

Systemic difference in the way subjects are selected that makes the study population different from the entire eligible population

Answer 23

Selection bias

Question 24

Patients with a certain medical history are more likely to participate in a study related to their condition, although they aren’t necessarily representative of the general population

Answer 24

Self selection bias

Question 25

Confounding variables

Answer 25

Factors that affect both the control group in the experimental group