Study designs Flashcards
Nutritional epidemiological studies:
made up of a risk fcator or exposure, the outcome or disease, the study is designed around a research question
Things to consider for a study design
Need to consider
* Population
* Strength and limitations of design
* Ethical issues
* Cost and time
How to represent a desired population
Once the reference population is identified, methods for selecting subjects should be developed
* Goal is to enroll a study group who will represent this identified population
confounding
example is “High Processed Food Diet and Heart Disease
confoundings are age smoking excericse
a test hypotheses
enabling testers to test a hypothesis is a further goal allows comparisons of subjects with different levels of independent variables. different methods that show comparison groups are shown the same way
independant variable
Independent variable
* The variable that is changed in a scientific experiment – “the input” * Examples: exposure to nutrient, physical activity levels
MAY BE MANIPULATED BY EXPERIEMENTER
dependent variable
The variable that will be measured in the scientific experiment – the “output”
* Often a disease e.g. occurrence of bowel cancer, CVD, hypertension, renal failure
CAN BE MEASURED
evidence of causation
Identifying the cause of disease to prevent it or cure it is a primary goal of epidemiology.
the six key criteria of causation
- Strength of Study Design
- Strength of Association
- Consistency of Association
- Temporal Relationship between Cause and Outcome
- Dose Response Relationship
- Biological Plausibility
evaluate the intervention
relevent to the study with the goal of evaluating an intervention eg drug treatment , surgical procedure
primary data collection methods
where the investigator is the first to collect the data
sources include medical eximnations and interviews
secondary data collection
DATA IS COLLECTED BY OTHERS
Types of primary studies
1.Descriptive studies : designs the occurance of an outcome
2. Analytic studies describes the association between exposure and outcome
observational studies
cross sectional, case series, case-control studies, cohort studies
- identify participants
- observe and record characteristics
- look for associations
experiemental studies
before and after studies, comparative trials, randomised trials
- identify participants
-place in common context
-intervene
- observe/evaluate effects of intervention
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ecological study
compares rates of exposures and diseases in different populations using aggregate data not individual data
may compare data on diet and disease across countries
important for differentiating between genetic and environmental issues.
cross sectional studies
carried out in a single point in time, often used to assess prevelence of a situation, to describe a current situation
unlike ecological studies it is known those with the disease is due to exposure
case control study
People with a disease (cases) are compared to similar people without a disease (controls) to determine if the cases are more likely to have particular exposures that the controls.
* A case-control study is always retrospective because it starts with an outcome then traces back to investigate exposures.
cohort studies
Follow a group of individuals over time to assess the incidence of a disease (or some other outcome)
* Are used to describe the effect of exposure to one or more factors of interest (potential risk factors) on the incidence of the outcome
* Can be prospective or retrospective/historical
What is a randomized control trial
randomised= ensures that treatment groups are similar, at the start of the trial
controlled=control group allows us to conclude that any improvement in outcome is due to the test treatment rather than some other factor
Comparison is usually between a new regimen/ intervention and an existing standard of care or placebo
* Provides most convincing evidence of relationship between exposure and effect
Types of RCT
1. Parrell group :
- Crossover trial
1.each patient is randomised to recieve only one of the two different strategies
each patient recives one stratgey first and then the other randomised
2.
