Observational Study

Question 1

What is a study?

Answer 1

A scientific process of answering a question using data from a population
e.g. does smoking cause cancer?
Is there more dieseae in an area than another?

Question 1

Process for epidemiological study

Answer 1

Identify a study question
Select a study type
Collect and analyze data using a suitable statistical method
interpret results
report findings

Question 2

Ecological Study

Answer 2

group of people
groups can be as small as people in a house or as large as everyone in a country
results apply to a group, not to indiiduals
Useful for comparing health of populations in different places
Also useful for generating questions and highlighting issues that lend themselves to future investigation

Question 3

Case Series

Answer 3

describes the characteristics of a group of people who have the same disease or the same exposure
aim is to understand the demographics, clinical presentation, prognosis, or other characteristics of people with a particular disease, or to describe something unusual

Question 4

Cross Sectional Study

Answer 4

AKA prevalence studies
measures health info at a given point of time from a selected population –> giving a snapshot of their health
usually involves a health questionnare
Health surveys are an example of a cross sectional study
important that selected population is representative of the total population
relatively inexpensive, relatively easy to conduct, can provide info on multiple exposures and outcomes, good way of assessing the health needs of a population
BUT because info is collected at a singled point in time, cannot be used to determine causality

Question 5

Case Control Study

Answer 5

group of people with disease (cases) and control group without (control) (similar to those with cases, but lack disease)
Both groups asked abt previous exposures to risk factors
Odds of being exposed (case) / Odds of being exposed (control) = Odds Ratio (OR)
OR > 1 = associated with diesease
OR = 1 = no association
OR < 1 = protective factor

commonly used in foodborne outbreak investigations

Advantages:
quick + cheap, good for uncommon diseases
Disadvantages:
not good for rare exposures, control selection, recall may be problem

retrospective

Question 6

Cohort Studies

Answer 6

A group of people is followed over a period of time to see what happens to them + info abt risk factors is collected
can compare outcome in those who were exposed to a particular risk factor vs those who were not exposed

Relative Risk (RR) = risk of disease (exposed) / risk of disease (unexposed)
RR>1 = exposure associated w increased risk of disease
RR = 1 = risk is the same
RR < 1 = risk is lower

Advantages:
time sequence can be determined - useful when trying to determine causality
info abt several diff outcomes/risk factors can be collected at the same time - allows for sub-analysis

Disadvantage:
high cost
not suitable to study rare diseases
ensuring that people who start study stay till the end

prospective

Question 7

Interventional Study

Answer 7

Intervention done on a group of people and the outcome is studied
Randomized Control Study (best interventional study)
- random allocation of if patient receives intervention vs no intervention (control)
- two groups are compared based on outcomes
- Ideally is double blind (participants and investigators dont know who is getting what)
-Advantages: can provide good evidence that the intervention led to an outcome (causality), randomization (both groups have equal chance of receiving the intervention and both groups have similar characteristics)
-Disadvantages: expensive, many participants, not always suitable (in situations where witholding an intervnetion may be unsuitable or unethical)

Question 8

Summaries

Answer 8

1. Systematic review: identifies all the relevant studies, assesses their quality, synthesizes and interprets the findings, presents an impartial summary of evidence
2. Meta-analysis: uses data from all studies that have addressed the same question with a similar design and uses data to do a combined statistical analysis to produce a single summary result

Question 9

Analytical + Descriptive studies

Answer 9

Descriptive - generates hypotheses
Ecological, case series/reports, cross-sectional
Analytical - tests hypotheses
cohort, case-control