Stats cram

Question 1

Purpose of cross sectional study

Answer 1

Prevalence of exposure and disease at specific point in time

Question 2

Purpose of ecological study

Answer 2

Assess link between exposure and outcome
Used if outcome of study is rare

Question 3

Purpose of cohort study

Answer 3

Studies incidence rate and whether exposure is associated with outcome of interest
Used for large study populations
May be prospective or retrospective

Question 4

Purpose of RCT

Answer 4

Determines possible effect of specific intervention on population
Minimises bias

Question 5

Variants of RCT

Answer 5

• Parallel group design - participants remain in assigned groups for entire duration
• Crossover design - participants switch groups during study
• Factorial design - experimental study design in which multiple interventions are studied simultaneously
• Cluster design - experimental study design in which unit of randomisation is a group rather than individual participant

Question 6

Types of errors

Answer 6

Type 1 error - null hypothesis rejected when it is actually true, or alternative hypothesis is accepted (false positive error)
Type 2 error - null hypothesis is accepted when it is actually false (false negative error)

Question 7

Statistical power

Answer 7

1 - probability of type 2 error

Question 8

P-value

Answer 8

Compared to significance level
Chance of type 1 error

Question 9

Purpose of T-test

Answer 9

Calculates difference between means of two samples
Unpaired - two different group samples at same time
Paired - same group samples at two different times

Question 10

Purpose of ANOVA

Answer 10

Extension of t-test
Calculates difference between more than 2 groups

Question 11

Purpose of Spearman correlation coefficient

Answer 11

Calculates relationship between two variables according to rank

Question 12

Purpose of Mann-Whitney U test

Answer 12

Compares ordinal, interval or ratio scales
Calculates whether two independently chosen samples originate from sample population

Question 13

Purpose of Wilcoxon test

Answer 13

Rank sum - Compares means between groups of different sizes
Signed rank - compares means between pairs of scores that can be matched

Question 14

Purpose of Kruskal-Wallis H test

Answer 14

Compares multiple groups by testing null hypothesis

Question 15

Purpose of binomial test

Answer 15

Examines whether observed frequency of event with binary outcomes is statistically probable or not

Question 16

Purpose of Chi-square test

Answer 16

Compares distribution of two categorical variables

Question 17

Purpose of Fisher exact test

Answer 17

Calculates difference between frequencies in a sample - used if study sample is small

Question 18

Odds ratio definition

Answer 18

Comparison of odds of an event occurring in one group compared to another group

Question 19

Hazard ratio definition

Answer 19

Measure of effect of intervention on outcome at any given point during study period

Question 20

Relative risk definition

Answer 20

Likelihood of an outcome in one group exposed to potential risk factor compared to risk in another group