Research Concepts

Question 1

Retrospective Studies

Answer 1

• Looking back at data already collected.
• Tend to miss data.

Question 2

Prospective Studies.

Answer 2

Collect data as study goes on

Question 3

Experimental Study

Answer 3

You are manipulating something to get information.

Question 4

Observational Study

Answer 4

• Simply looking at data, not actually manipulating anything to get information.
• Cannot make claims about causation.

Question 5

What are Case Control studies, what do they look at, and what measure of statistics is used.

Answer 5

• Compare case (has disease) with control (doesn’t have disease).
• Cannot tell prevalence as you are selecting cases so prevalence artificially high.
• Tend to be experimental studies.
• Looking at “What is the Frequency of exposure? in those with disease and those without disease.
• Use Odds Ratio.

Question 6

Cohort Study

Answer 6

• Take cohort as it comes, you aren’t selecting particular cases with disease.
• Reflects true prevalence.
• Tend to be observational studies.
• Looking at “Is the outcome occuring?” in those exposed and those not exposed.
• Use Relative Risk.

Question 7

Intention to Treat

Answer 7

• Analysis includes all participants, no matter if they completed trial or not.
• Use if wanting to know if clinician should use treatment.

Question 8

Per protocol Design

Answer 8

• Analysis only includes participants who complete trial.
• Use if wanting to know mechanism of drug (i.e. need people who have completed treatment).

Question 9

Descriptive statistics

Answer 9

• Describe the sample data.
• Reduce many numbers down –> fewer numbers.
• E.g. mean, median, standard deviation.
• Sample statistics.
• Use english letters (e.g. M, SD)

Question 10

Inferential statistics

Answer 10

• Use sample statistics to predict population parameters.
• Use greek letters (e.g. mu, delta).

Question 11

Type 1 error

Answer 11

• Incorrectly reject the null hypothesis –> accept working hypothesis.
• The probability is the alpha-level (usually 0.05).
• False positive (e.g tell a male he is pregnant or e.g use a drug which is ineffective or has adverse effects).
• Due to P value.

Question 12

Type 2 error

Answer 12

• Incorrectly retain the null hypothesis –> working hypothesis is rejected.
• The probability is the beta level (often 0.2).
• False negative (e.g tell a pregnant women she isn’t pregnant or e.g. don’t use a drug which is effective for a particular disease).
• Due to Statistical power i.e. sample size.

Question 13

Confidence intervals

Answer 13

• We can be 95% confident that the true parameter sits between these two values.
• If we repeated the procedure (maths calculation to get confidence interval) many times over again, the confidence interval would capture the true value. 95% of the time.
• Never the probability of the parameter having a certain value.

Question 14

Relative risk (risk ratio)

Answer 14

ratio of the probability of outcome in one group to the probability of the outcome in another group
RR = (TE / (TE + TN)) / (CE / (CE + CN))
TE = treatment with events.
TN = treatment, non-events.
CE = control with events.
CN = control, non-events

Question 15

What are the Canadian Task force Level of evidence?

Answer 15

I: At least 1 RCT with proper randomisation.
II.1: Well designed cohort of case-control study.
II.2: Time series comparison or dramatic results from uncontrolled studies.
III: Expert opinion.

Question 16

What are the levels of evidence from Sackett?

Answer 16

I: Large RCTs with clear cut results.
II: Small RCTs with unclear results.
III: Cohort and case-control studies.
IV: Historical cohort or case-control studies.
V: Case series, studies with no controls.

Question 17

What are the levels of evidence for Prognostic studies?

Answer 17

I: High quality prospective cohort study with adequate power or systemic review of these studies.
II: Lesser quality prospective cohort, retrospective cohort study, untreated controls from RCT, or systematic review of these studies.
III: Case-control study or systematic review of these studies.
IV: Case series.
V: Expert opinion, case report or clinical example, or evidence based on physiology, bench research or “first principles”.

Question 18

What are the levels of evidence for therapeutic studies?

Answer 18

1A: Systematic review (with homogeneity) of RCTs.
1B: Individual RCT (with narrow confidence intervals).
1C: All or none study.
2A: Systematic review (with homogeneity) of cohort studies.
2B: Individual cohort study (including low quality RCT e.g. < 80% follow-up).
2C: “Outcomes” research, ecological studies.
3A: Systematic review (with homogeneity) of case-control studies.
3B: Individual case-control study.
4: Case series (and poor quality cohort or case-control study).
5: Expert opinion without explicit critical appraisal or based on physiology bench research or “first principles”.

Question 19

What are the Grade Practice Recommendations?
-Grade A

Answer 19

• Strong recommendation.
• Level I evidence or consistent findings from multiple studies of levels II, III or IV.
• Clinicians should follow a strong recommendation unless a clear and compelling rationale for an alternative approach is present.

Question 20

What are the Grade Practice Recommendations?
-Grade B

Answer 20

• Recommendation.
• Levels II, III or IV evidence and findings are generally consistent.
• Generally clinicians should follow a recommendation but should remain alert to new information and sensitive to patient preferences.

Question 21

What are the Grade Practice Recommendations?
-Grade C

Answer 21

• Option.
• Levels II, III, or IV evidence, but findings are inconsistent.
• Clinicians should be flexible in their decision-making regarding appropriate practice, although they may set bounds on alternatives; patient preference should have a substantial influencing role.

Question 22

What are the Grade Practice Recommendations?
-Grade D

Answer 22

• Option.
• Level V evidence: little or no systematic empirical evidence.
• Clinicians should consider all options in their decision making and be alert to new published evidence that clarifies the balance of benefit vs harm; patient preference should have a substantial influencing role.