Lecture 3 Flashcards
(27 cards)
What are the 2 categories of the study designs
Experimental and observational
What are the studies of studdies
Meta analyses and systematic reviews
What are the experimental studies
Randomised control studies and quasi experimental studies
What are the observational studies
Cohort, case control and case reports
What are the observational studies good for?
Studying various problems
What are cohort studies used for
Used to study incidence, causes and prognosis, they measure events in chronological order and are used to distinguish cause and effect.
What are cross sectional studdies
Used to determine prevalence usually quick and easy but it can not distinguish between cause and effect
What are case control studies
Compares groups retrospectively, the seek to identify possible predictors of outcome and its useful for studying rare diseases or outcomes, it’s often used to generate hypotheses that can then be studied via prospective cohort
What is the dunedin study
It’s a cohort study that followed the lives of 1037 babies born between April 1st 1972 to 31sf march 1973 since their birth.
What is the mechanism for a cohort study
And how does it differ from clinical trials
•Cohort studies are longitudinal, observational studies, which investigate predictive risk factors and health outcomes.
•They differ from clinical trials, in that no intervention, treatment, or exposure is administered to the participants. The factors of interest to researchers already exist in the study group under investigation.
•Study participants are observed over a period of time. The incidence of disease in the exposed group is compared with the incidence of disease in the unexposed group.
•Because of the observational nature of cohort studies they can only find correlation between a risk factor and disease rather than the cause
Why can cohort studies be useful
There is a persuasive hypothesis linking an exposure to an outcome.
•The time between exposure and outcome is not too long (adding to the study costs and increasing the risk of participant attrition).
•The outcome is not too rare.
What are the stages of a cohort study
A cohort study starts with the selection of a group of participants (known as a ‘cohort’) sourced from the same population, who must be free of the outcome under investigation but have the potential to develop that outcome.
•The participants must be identical, having common characteristics except for their exposure status.
•The participants are divided into two groups – the first group is the ‘exposure’ group, the second group is free of the exposure.
What are the 2 types of cohort studies and explain them
Prospective and retrospective
Prospective:
•The two groups of cohorts (exposed and un-exposed) are followed prospectively over time to track the development of new disease.
•Example: In a prospective cohort study researchers compared four different groups of women (two at-risk groups, two low-risk groups) to investigate which groups were more likely to develop PTSD(Post-traumatic stress disorder ) symptoms after a birthing event.
Retrospective: Cohorts are defined from a previous point in time, and are not followed up in the future.
•Information or data is collected from past clinical records and the outcome of interest is investigated.
•Useful for tracking the progress of a disease with a long latency period.
•Example: In a retrospective cohort study researchers used previously collected data to investigate whether there was an association between birth experience and subsequent maternal care-giving attitudes and behaviour over a 12-month period
What are the advantages of a cohort study
The only observational study design that directly investigates risk of disease and the factors contributing to it.
•Ethically safe.
•Multiple outcomes can be measured.
•They are good for rare types of exposures, e.g. an exposure to a chemical spill in a factory.
What are the disadvantages of a cohort study
Not appropriate for rare diseases or those that take a long time to develop e.g. mesothelioma.
•Not appropriate for studying multiple exposures.
•Can be costly and time consuming.
Cohort study calculation
relative risk formula: RR = incidence rate among exposed/ incidence rate among non exposed
Interpretation: Measures the risk of developing an outcome (e.g., disease) in the exposed group relative to the non-exposed group.
- Attributable Risk (AR):
•Formula:
AR=Incidence rate in total population−Incidence rate among non-exposed
•Interpretation: Estimates the excess risk of the outcome attributable to the exposure.
What is the mechanism for cross sectional studies
oss sectional studies are used to determine prevalence.
They are relatively quick and easy but do not permit distinction between cause and effect.
Cross-sectional studies look at a population at a single point in time, like taking a slice or cross-section of a group, and variables are recorded for each participant.
This may be a single snapshot for one point in time or may look at a situation at one point in time and then follow it up with another or multiple snapshots at later points; this is then termed a repeated cross-sectional data analysis
Which clinical questions does a Cross-Sectional study best answer
Cross-sectional study designs are useful when:
•Answering questions about the incidence or prevalence of a condition, belief or situation.
•Establishing what the norm is for a specific demographic at a specific time.
For example: what is the most common or normal age for students completing secondary education in Victoria?
•Justifying further research on a topic. Cross-sectional studies can infer a relationship or correlation but are not always sufficient to determine a direct cause. As a result, these studies often pave the way for other investigations.
Pros of cross sectional study
Efficient and fast option for research.
•Represents the population without requiring exact participant continuity.
•Can use less labor-intensive data collection methods like surveys or questionnaires.
•Enables investigation of multiple variables simultaneously.
Observational Benefit:
•Ethically explores harmful situations without imposing conditions on participants.
Cons of a cross Sectional study
Cannot establish direct causation, only correlations.
•Unsuitable for tracking changes over time; longitudinal studies are more appropriate.
•Challenging to study rare diseases due to difficulties in finding enough participants.
Describe case control studies
In a Case-Control study there are two groups of people: one has a health issue (Case group), and this group is “matched” to a Control group without the health issue based on characteristics like age, gender, occupation.
In this study type, we can look back in the patient’s histories to look for exposure to risk factors that are common to the Case group, but not the Control group.
These studies estimate the odds between the exposure and the health outcome, however they cannot prove causality.
Case-Control studies might also be referred to as retrospective or case-referent studies.
Stages of case control studies
This diagram represents taking both the case (disease) and the control (no disease) groups and looking back at their histories to determine their exposure to possible contributing factors.
The researchers then determine the likelihood of those factors contributing to the disease.
What are the retrospective case control studies
➢Group of disease cases is identified exposure history is compared with that of a control group from the same population;
➢Most desirable for studying diseases that have low prevalence or that require a long induction or leant period to develop, when exposure date are difficult to obtain, or when the study population is dynamic;
Case control advantages and opportunities
Advantages:
•Helps identify the source of existing illnesses or epidemics.
•Cost-effective and quick, requiring no specialized equipment.
•Patients already have the health condition, reducing ethical concerns.
•Examines multiple risk factors like environment, work, and diet.
Opportunities:
•Particularly useful for investigating rare conditions, where causing disease via trials is unethical.
•Identifies outbreak origins by examining common exposures in case histories.
•Explores various patient exposures to pinpoint potential causes when no single factor stands out
