Experimental Design

Question 1

What are the types of observational studies?

Answer 1

> cross sectional studies
longitudinal studies
cohort studies

Question 2

Whats a cross-sectional study?

Answer 2

an observational study that analyses data from a population at a single point in time

Question 3

what are the advantages of a cross-sectional study?

Answer 3

1) quick and inexpensive
2) best way to determine prevalence
3) allows collection from a large pool of subjects
4) useful for estimating disease burden and identifying associations

Question 4

what are the disadvantages of a cross-sectional study?

Answer 4

1) unable to measure incidence
2) difficult to determine causality
3) can’t investigate temporal relationships
4) susceptible to bias (non-response + recall)

Question 5

what are the advantages of a longitudinal study?

Answer 5

1) can establish sequence of events and cause-and-effect relationships
2) prospective studies eliminate the risk of recall bias

Question 6

what are the disadvantages of a longitudinal study?

Answer 6

1) time consuming and more expensive
2) potential insights may take a long time to be discovered
3) participants may drop out

Question 7

what are the advantages of Prospective Cohort Studies?

Answer 7

1) able to control design, sampling, data collection, and follow-up methods
2) can measure all variables of interest

Question 8

what are the advantages of retrospective Cohort Studies?

Answer 8

1) time and cost efficient
2) easy to obtain a large sample

Question 9

what are the disadvantages of Prospective Cohort Studies?

Answer 9

1) may be expensive and time consuming
2) questionable ethics if the exposure being studied is harmful/no treatment

Question 10

what are the disadvantages of retrospective Cohort Studies?

Answer 10

1) less control over variables
2) susceptible to information and recall bias

Question 11

what are the advantages of case-control studies?

Answer 11

1) efficient for rare diseases or outcomes
2) require smaller sample sizes, faster and less expensive
3) if multiple exposures lead to a single outcome, these are well incorporated = rare outcomes.

Question 12

what are the disadvantages of case-control studies?

Answer 12

1) susceptible to observer bias, recall, and interviewer bias
2) can be contradictory
3) selection of controls can be challenging (selection bias)
4) difficult to establish temporal relationships.

Question 13

Why is the use of appropriate sampling methods necessary?

Answer 13

1) allows a representative sample to be drawn
2) reduces bias
3) can reduce cost
4) ethical implications: burden of research is fairly distributed
5) allows accurate conclusions to be drawn

Question 14

what are the types of probabilistic sampling?

Answer 14

1) simple random
2) stratified
3) cluster
4) systematic

Question 15

what is simple random sampling?

Answer 15

1) a list of all individuals in target population is made
2) each individual assigned an identifier
3) participants are randomly selected using this
4) ensures all individuals have equal and independent probability of inclusion

Question 16

what is stratified sampling?

Answer 16

1) divide population into strata (age, weight, race etc.)
2) take random samples within these

Question 17

what is cluster sampling?

Answer 17

1) Define the population
2) Cluster the population
3) Randomly select n clusters
4) Collect data from the n clusters

Question 18

what is systematic sampling?

Answer 18

samples members from a larger population using a fixed starting point, moving in intervals

Question 19

what are the advantages of probabilistic sampling?

Answer 19

1) should be representative and generalisable
2) should reduce selection bias
3) ensures statistical validity

Question 20

what are the disadvantages of probabilistic sampling?

Answer 20

1) can be resource intensive
2) requires a complete list of population
3) stratified and multi-stage sampling require complex designs and analysis

Question 21

What are non-probabilistic sampling methods?

Answer 21

1) convenience sampling
2) quota sampling
3) snowball sampling

Question 22

whats quota sampling?

Answer 22

relies on the non-random selection of a predetermined number or proportion of units.

Question 23

what is snowball sampling?

Answer 23

when existing participants recruit future participants from their own network.

Question 24

What are the advantages of non-probabilistic sampling?

Answer 24

1) more practical, reduces time and resources spent acquiring a sample.
2) targeted sampling allows researchers to focus on specific populations of interest

Question 25

What are the disadvantages of non-probabilistic sampling?

Answer 25

1) limits generalisability = less representative 2) introduces various biases reducing validity

Question 26

what are the disadvantages of survey data collection?

Answer 26

1) challenging to ensure questions are clear and unbiased 2) low participation can introduce bias

Question 27

what are the advantages of interview data collection?

Answer 27

1) can gain a good depth of data 2) can clarify responses; more flexible

Question 28

what are the disadvantages of interview data collection?

Answer 28

1) require time and skilled personnel = resource intensive 2) interviewer bias

Question 29

what are the advantages of medical research data collection?

Answer 29

1) comprehensive clinical info over time 2) cost-effective to use existing records

Question 30

what are the disadvantages of medical research data collection?

Answer 30

1) data quality; variation and inconsistencies 2) accessibility and privacy issues

Question 31

what is sampling bias?

Answer 31

arises when the sampling method systematically favors certain individuals

Question 32

what is recall bias?

Answer 32

occurs in retrospective studies; patients may misremember info, reducing accuracy

Question 33

what is volunteer bias?

Answer 33

arises when individuals who choose to participate in a study differ systematically from those who do not

Question 34

what is survivorship bias?

Answer 34

Occurs when researchers focus only on those who pass some sort of selection process vs those who didn't = only study a subset of the population

Question 35

what is interview bias?

Answer 35

stems from the person conducting the study either in the way they ask questions or their preconceived personal biases (prejudice)

Question 36

what is response bias?

Answer 36

situations where people do not answer questions truthfully because of a perceived 'correct' answer

Question 37

what are the types of response bias?

Answer 37

1) Acquiescence bias; always answering yes 2) social desirability bias 3) courtesy bias; being polite over honest 4) question-order bias 5) extreme response bias

Question 38

what are the impacts of bias?

Answer 38

1) invalid results 2) reduced generalisability 3) misguided clinical decisions

Question 39

What is the purpose of randomisation?

Answer 39

1) ensures causality 2) minimises selection bias 3) balances both known and unknown confounders

Question 40

When is an active control used?

Answer 40

when there is a well-established treatment; to show that the experimental treatment is superior

Question 41

when is a placebo control used?

Answer 41

when an effective treatment for a disease does not already exist for comparison.

Question 42

what are the advantages of an RCT?

Answer 42

1) directly comparable results; causal inference 2) minimises bias 3) improves statistical reliability

Question 43

what are the disadvantages of an RCT?

Answer 43

1) resource intensive; time and money 2) results may not mimic real-life due to strictly controlled conditions 3) beneficial treatment may be being withheld

Question 44

what are the advantages of a cross-over design?

Answer 44

1) fewer participants needed 2) reduces variability; more precise estimate of treatment effects

Question 45

what are the disadvantages of a cross-over design?

Answer 45

1) cannot analyse long-term effects 2) carry over effect may interfere with results

Question 46

what is as treated analysis?

Answer 46

participants are analysed based on the treatment they received rather than the group they were initially assigned to.

Question 47

what is per protocol analysis?

Answer 47

only including those who adhered to protocol and initial group assignment.

Question 48

what is intention to treat analysis?

Answer 48

everyone involved in study is included in the analysis, according to their original group assignment. 1) avoids bias and maintains integrity of randomisation 2) allows real-life conclusions to be drawn