Lecture 4

Question 1

IMRAD

Answer 1

Introduction- why was the study done?
Methods- How was it conducted? 
Results- What were the outcomes?
Analysis- How was the data treated?
Discussion- What does the data mean?

Question 2

When to use IMRAD

Answer 2

When reviewing a paper.

Question 3

The methods section is key to making sure you have a quality study. What should be included in the methods section?

Answer 3

Originality 
Who is being studied? 
Was it well designed?
Did the study minimize systematic bias?
Did the study have enough power? Are there statistical biases?

Question 4

some key words to consider when looking at the originality of the methods section when reviewing a paper

Answer 4

Robustness- may increase with larger sample size or longer duration
Rigor: When addressing criticisms of previous studies
Improved generalizability if you study additional populations.

Question 5

How to increase robustness of a methods section

Answer 5

may increase with larger sample size or longer duration

Question 6

How to improve rigor of a methods section

Answer 6

When addressing criticisms of previous studies

Question 7

How to improve generalizability of a methods section

Answer 7

Study additional populations.

Question 8

How to confirm validation of a methods section

Answer 8

Validation will confirm repeatability of previous study findings.

Question 9

Why is it important to consider who is being studied in the methods section?

Answer 9

Should consider how the subjects were recruited, inclusion and exclusion criteria, and population from which they were drawn from. Are they representative?

Question 10

Recruitment methods of subjects influence ____

Answer 10

Inference: drawing conclusions based on data found.

Who, where, and time frame are all relevant to outcomes.

Question 11

How to determine if the study was well designed based off methods section

Answer 11

Consider the event being studied
Consider the outcome measures- did they use surrogate endpoints or objective measures (should be objective in most EBM studies)
Assess validity of the outcome measures- did they measure what they said they were measuring?

Question 12

What is the difference between statistical significance and clinical significance?

Answer 12

Statistical significance is objective. Determined by a test.

Clinical significance is somewhat subjective. Knowledge regarding the clinical measure report is necessary to evaluate significance.

Question 13

Systematic bias

Answer 13

Anything which erroneously influences the conclusions about groups and distorts comparisons.

Bullseye with all hits off center.

All studies may contain systematic bias, but each study design requires different steps to avoid or minimize.

Question 14

How can you avoid systematic bias?

Answer 14

Do a RCT: gold standard, should theoretically avoid systematic bias.

It AVOIDs, but not minimizes completely. Some biases that can still occur in a RCT include:

Selection bias, performance bias, exclusion bias, and detection bias.

Question 15

Selection bias (may occur in RCT)

Answer 15

Incomplete randomization to groups.

Question 16

Performance bias (may occur in RCT)

Answer 16

TREATMENT varies apart from intervention (what you actually did)

Question 17

Exclusion bias (may occur in RCT)

Answer 17

Differences in WITHDRAWALS from each group. Ex: people from placebo group may withdrawal bc they don’t think they are getting anything out of the study. People in test group may withdrawal due to side effects of drugs.

Question 18

Detection bias (may occur in RCT)

Answer 18

Differences in outcome assessments.

Question 19

Why non-randomized controlled trials lead to systematic bias

Answer 19

If people put themselves into groups, they might share some personality traits or common interests. This will cause an overestimated effect of your trial.

Question 20

What is challenging about a cohort study?

Answer 20

Control group selection can be challenging. People who weren’t exposed.

The goal is to find two identical groups in age, gender, socioeconomic status, and coexisting illness (or lack in control group)

Question 21

How can retrospectively designed tests induce systematic bias?

Answer 21

Recall bias. Lack of control over data that was collected.
Definition of condition may change over time- misclassification is a bias that may skew findings (blood pressure example)

Question 22

Two of the main ways to prevent statistical bias

Answer 22

Adequate sample size and power.

Question 23

Power

Answer 23

The likelihood of deleting a statistically significant difference if the study hypothesis is true. This is also referred to as test sensitivity.

Question 24

Relationship between effect and power

Answer 24

inverse. Small effect = high power.

Question 25

How is effect size chosen?

Answer 25

By the investigator

Question 26

What to consider when choosing a sample size and power?

Answer 26

Clinical significance and statistical significance

Question 27

Sample sizes needed for a larger effect size

Answer 27

Larger effect size= larger difference between the control and test groups= need fewer people to detect.

Question 28

Sample sizes needed for smaller effect size

Answer 28

Need more people to detect smaller effect size. More sensitivity.

Question 29

Type I (alpha) error in statistical bias

Answer 29

False positive. Rare.

Question 30

Type II (beta) error in statistical bias

Answer 30

False positive.

Ex: Beta of 10%
Power = 1-B
1-0.10= 90%

Question 31

Study power should be a minimum of

Answer 31

80%-90%

Question 32

Formula to determine power based on Beta (Type II error, statistical bias)

Answer 32

Power = 1 - B

Question 33

Rule of thumb. Adequate follow up %

Answer 33

Better than 70% return for follow up.

Question 34

Reasons why subjects may not return to follow up (need 70% or better return)

Answer 34

Failure to follow criteria
Adverse effects 
Loss of motivation
Clinical reasons
Death

Question 35

How blinding can reduce performance (treatment) bias?

Answer 35

If the investigator is not blinded, may bias treatment towards those perceived as needing it most.

If participants are not blinded: may alter their behavior.

Question 36

How binding can reduce treatment (withdrawal) bias?

Answer 36

If investigators are not blinded, they may exclude subjects from analyses that didn’t get ideal results.

Subjects who withdraw may influence results.

Question 37

Intent to treat analysis

Answer 37

Includes all subjects up until the point they either finish or withdraw from the study.

If withdrawals are not induced, the study is biased in the direction of the intervention.

Question 38

Efficacy (per protocol) analysis

Answer 38

Opposite of intent to treat. Examines only the effect of the treatment being studied and subjects who completed the protocol. Creates two cohorts even if a RCT design is used.

Only ones who followed the rules are included in the analysis.