Stats related

Question 1

What is type 1 error?

Answer 1

occurs when we incorrectly reject a null hypothesis that is true (false positive) e.g. positive pregnancy test in a male

Question 2

What is a type 2 error?

Answer 2

occurs when we fail to reject (accept) a null hypothesis that is false (false negative) e.g. negative pregnancy test in a pregnant woman

Question 3

What is statistical significance (alpha)?

Answer 3

the probability of a type 1 error occurring. This can be pre-determined as the acceptable amount of Type 1 error or alpha. Most likely to be 0.05

Question 4

What is study power?

Answer 4

Study power is the ability of a study to find a difference between the two arms.

It is predetermined to reduce type 2 error.
Most studies are powered to 0.8

Question 5

What can researchers do to increase power?

Answer 5

Increasing power reduced type 2 error and this is achieved by:
1. Increasing sample size
2. increasing effect sizes (what difference in outcomes is seen to be representative of a difference)
3. increase significance levels (alpha)

Question 6

What is a confounder?

Answer 6

a variable that influences both the dependent variable and independent variable, causing a spurious association. It can also be a source of bias

Question 7

What does a 95% confidence interval convey?

Answer 7

95% confident that the true outcome effect lies between X and Y

Question 8

What affects the confidence interval of a sample mean?

Answer 8

Standard deviation, sample size, and the type of sample data distribution

Question 9

What studies are best suited for using odds ratios?

Answer 9

Case-control studies

Question 10

How would you interpret a risk ratio of 2?

Answer 10

The exposure group has 2-times the risk of developing the outcome compared to the non-exposure group

Question 11

How do you interpret a p-value of 0.05?

Answer 11

The chance of the observed difference occurring by random chance is 5%. A p-value less than 0.05 is often noted as being statistically significant.

Question 12

When comparing baseline characteristics between two groups, what do you want your p-value to be?

Answer 12

As close to 1 as possible, to signify no significant difference in a baseline characteristic between the two groups

Question 13

What is confounding by indication?

Answer 13

confounding caused by the indication of the intervention. For example, C-sections are 4.3 times more likely to result in maternal death compared to NVD. The confounding factor is the reason for a C-section.

Question 14

True or False. Does standardization reduce confounding and other forms of bias?

Answer 14

True

Question 15

What is a null hypothesis?

Answer 15

A null hypothesis assumes that any observed difference is a result of random chance and that no association exists

Question 16

How are cohort studies different from case-control studies?

Answer 16

They are both examples of observational (non-interventional) studies
Cohort study you are comparing an exposure (most often a risk factor or disease) to a control (do not have the risk factor or disease)) and measuring their effect on an outcome. These are more likely to be prospective and measure effect as risk ratios
Case-control study you know what the outcome is (a disease for example) and you are trying to determine the effect of a risk factor. These are more likely to be retrospective and measure effect as odds ratios.

Question 17

What is critical appraisal?

Answer 17

a systematic process used to identify the strengths and weaknesses of a research article to assess the usefulness and validity of its research findings

Question 18

What are the six key components of critical appraisal?

Answer 18

(1) Assessing the appropriateness of the study design for the research question;
(2) Careful assessment of the key methodological features of this design;
(3) Suitability of the statistical methods;
(4) Accuracy of subsequent interpretation;
(5) identify potential conflicts of interest;
(6) Relevance to their surgical practice

Question 19

What is the evidence hierarchy of medical literature?

Answer 19

Level 1:
- A: Systemic review of RCT
-B: High quality RCT
-C: RCT
Level 2:
- A: Systemic review of cohort studies
- B: Cohort study
- C: Outcome research
Level 3:
- A: Svstemic review of case control studies
- B: Case control study
Level 4: Case series
Level 5: Expert opinion

Question 20

What is sensitivity?

Answer 20

The ability of a test to capture all individuals with a disease

Question 21

What is specificity?

Answer 21

The ability of a test to exclude those who do not have a disease

Question 22

What are the different types of randomization?

Answer 22

Simple, blocked, stratified, minimized

Question 23

What is p-value?

Answer 23

The probability of the null hypothesis being true

Question 24

What influences the p-value?

Answer 24

(1) Sample size (the larger a sample size, the more likely a difference will be detected);
(2) Magnitude of effect (a larger magnitude of effect will likely pick up a difference and therefore reduce the p-value;
(3) Spread of data (the bigger the standard deviation, the more spread, and the lower the p-value)

Question 25

What is PRISMA?

Answer 25

Stands for **Preferred Reporting Items** for Systematic Reviews and Meta-Analysis. It is an evidence based **minimum set of items** for reporting in systematic reviews and meta-analyses via a **27-point check-list** and **flow chart**

Question 26

What are the six main components of the PRISMA checklist?

Answer 26

Interrogation of: 1) abstract 2) introduction 3) **methods** - eligibility criteria, databases used, search terms used, screening process for choosing studies, risk of bias assessment tool 4) **results** - use of PRISMA flow diagram including why studies were excluded, summary of the study characteristics + results, bias assessment outcome 4) **discussion** - interpretation of results, limitations of studies used, limitations of the review, implications of results 5) if a **protocol** was followed and where to find it 6) conflicts of interests

Question 27

What are the benefits of PRISMA?

Answer 27

(1) Demonstrates the quality of the review. (2) allows readers to assess strengths and weaknesses. (3) permits replication of review methods.

Question 28

What is incidence and prevalence?

Answer 28

Prevalence - the proportion of population with the disease in a time point Incidence - the rate of new onset disease during a period of time

Question 29

What are four types of bias?

Answer 29

**Selection bias** - sampling bias and response bias **Observation bias** - failure to measure factors/outcomes accurately **Attrition bias** - number of drop outs differs in separate arms, those who are left are not representative of the original study **Confounding factors** - associated with exposure and outcome but independent.

Question 30

What are mean, median, and mode?

Answer 30

Mean - sum of all values / number of values in the data set Median - middle value of the data set Mode - most common value of the data set

Question 31

What is a meta-analysis?

Answer 31

A meta-analysis is the use of **statistical methods** to **combine results** of individual studies, usually RCTS. It allows researchers to have a more **precise estimation** of **treatment effect.**

Question 32

What is a systematic review?

Answer 32

Type of **secondary research** that involves **collating** all **empirical evidence** that fits **pre-specified eligibility criteria** in order to **answer** a specific research **question**. It uses **explicit, systematic methods** to minimizing bias, thus **providing** more **reliable findings** from which **conclusions** can be drawn and **decisions** made

Question 33

What are the advantages and disadvantages of meta-analysis?

Answer 33

Advantage 1. Greater **statistical power** to detect an effect than a single study 2. Combine results from several studies hence **less likely** to be influenced by **local factors.** Disadvantages 1. pooling results from several studies may not predict the results of a single large study. 2. if the source is poorly designed, the meta analysis will produce unreliable results.

Question 34

What is a Forest plot?

Answer 34

1. It is used to **demonstrate the results of meta analysis** 2. vertical line of no effect 3. Diamond = **point estimate of pooled result** 4. Horizontal line - 95% Cl; if CI crosses the vertical line of no effect, either sample size to too small or the result is not statically significant.

Question 35

What is a Randomised control trial?

Answer 35

A research design that allows: 1. Comparison of 2 or more possible interventions 2. Participants are randomly divided to separate arms Advantages: - Minimise the risk of allocation bias - Can be combined into systemic reviews/meta analysis to produce high level evidence Disadvantages: - Time and cost - Difficult on long term FU - Usually focus on a narrow area of patients condition

Question 36

What are the different phases of RCT?

Answer 36

Phase 1: 50-100 healthy volunteers to evaluate drug safety and side effects Phase 2: 100-300 patients with relevant illness to assess effectiveness and assess minimal dose Phase 3: Large RCT thousands of volunteers to confirm drug safety + effectiveness when compared to a placebo or standard treatment Phase 4. Postmarketing surveillance