exam Flashcards
what is an observational study
a study that analyzes a relationship in which there is no intervention and no randomization.
Researchers observe and analyze data without directly intervening or manipulating variables. It includes observing and collecting information about participants, behaviours, characteristics or outcomes
Examples:
studying the relationship between coffee and the risk of heart disease
those who smoke may eat fewer veggies and may drink more alcohol.
Pros:
Can be conducted in real world settings
Provide valuable insights into natural behaviours
Can study rare and long term outcomes
Cons
Cannot establish causality
May be subject to biases (selection:participants selected don’t represent the entire population accurately, recall: participants may not accurately remember or report their behaviours or outcomes, confounding; the observed association between variables may be influenced by other factors that were not accounted for.
Cannot control for all confounding factors
give 2 examples of confounding in an observational study
- high birth order causes down syndrome.
- studies were done though to find downsyndrome is actually related to maternal age, not birth order - does beta carotene prevent cancer?
- 9 large RCTs were done to find no relationship between beta carotene and cancer. However, the relationship was due to people in the observational study who ate more fruits and veg. the higher consumption of fruits and veg would likely increase beta carotene levels but was also the main factor in preventing cancer as opposed to the beta carotene preventing it.
this is why we CANNOT attribute causality to findings from observational studies. we can only report observed correlations or associations
what are the 3 types of observational studies?
cohort study
cross-sectional study
case control study
describe cohort study
give example
its an observational study
outcome is determined some time after the exposure or intervention.
- a type of longitudinal study—an approach that follows research participants over a period of time (often many years).
- Specifically, recruits and follows participants who share a common characteristic, such as a particular occupation or demographic similarity.
ex. those with high soy intakes and those with low soy intakes… follow them and monitor for presence of breast cancer (compare rates between groups).
ex. assess the impact of sun exposure on skin damage in beach volleyball players. During a tournament, players from one team wore waterproof, SPF 35 sunscreen, while players from the other team did not wear any sunscreen. At the end of the volleyball tournament players’ skin from both teams was analyzed for texture, sun damage, and burns. Comparisons of skin damage were then made based on the use of sunscreen. The analysis showed a significant difference between the cohorts in terms of the skin damage.
what is a strength of cohort studies?
temporality:
– the exposure is measured before the outcome, so we know the order of events
list the pros and cons of cohort studies
pros:
* temporality - knowing order of events
* Standardization of criteria/outcome is possible
* Easier and cheaper than a randomized controlled trial (RCT)
* not subject to recall bias
Cons:
* Cohorts can be difficult to identify due to confounding variables
* No randomization, which means that imbalances in patient characteristics could exist
* Blinding/masking is difficult
* Outcome of interest could take time to occur
what is a cross sectional study?
observational
outcome determined at the same time as the exposure or intervention
- doesnt tell order of events
- because the exposure and outcome measured at the same time, the direction is not clear in which came first
ex. Measure fruit and vegetable intakes in a group of grade 5 students
what is a case control study?
observational
outcome determined before exposure was determined
- retrospective study based on recall of exposure (lead to recall bias)
- compares patients who have a disease or outcome of interest (cases) with patients who do not have the disease or outcome (controls), and looks back retrospectively to compare how frequently the exposure to a risk factor is present in each group to determine the relationship between the risk factor and the disease.
give 2 examples of a case control study
There is a suspicion that zinc oxide, the white non-absorbent sunscreen traditionally worn by lifeguards is more effective at preventing sunburns that lead to skin cancer than absorbent sunscreen lotions. A case-control study was conducted to investigate if exposure to zinc oxide is a more effective skin cancer prevention measure. The study involved comparing a group of former lifeguards that had developed cancer on their cheeks and noses (cases) to a group of lifeguards without this type of cancer (controls) and assess their prior exposure to zinc oxide or absorbent sunscreen lotions.
This study would be retrospective in that the former lifeguards would be asked to recall which type of sunscreen they used on their face and approximately how often. This could be either a matched or unmatched study, but efforts would need to be made to ensure that the former lifeguards are of the same average age, and lifeguarded for a similar number of seasons and amount of time per season
ex. determine the association between metabolic syndrome and the beverages consumed by adults when they were children
explain pros and cons of case control studies
- Good for studying rare conditions or diseases
- Less time needed to conduct the study because the condition or disease has already occurred
- Lets you simultaneously look at multiple risk factors
- Useful as initial studies to establish an association
- Can answer questions that could not be answered through other study designs
Cons:
* Retrospective studies have more problems with data quality because they rely on memory and people with a condition will be more motivated to recall risk factors (also called recall bias).
* Not good for evaluating diagnostic tests because it’s already clear that the cases have the condition and the controls do not
* It can be difficult to find a suitable control group
what is selection bias
systematic difference in the groups that are compared
- occurs when the selection of data for analysis is not random and is instead influenced by certain factors
ex.
Volunteer bias: This occurs when the sample is self-selected, meaning that individuals volunteer to participate in a study or survey. This can lead to biased results as those who volunteer may not be representative of the population as a whole.
Sampling bias: This occurs when the sample is not representative of the population being studied. For example, if we only survey people in one region of the world, we may miss important differences in opinions or behaviors in other regions.
what is performance bias?
the care that is provided
ex. If the investigators know that an experimental group have been given an active drug, they may focus their attention on this group. The participants might receive more frequent exams and more diagnostic tests. This could result in the experimental group having a greater chance of a positive outcome — not because they have been given an active drug, but because they received very focused attention.
what is confounding bias?
exposure to other factors apart from the intervention of interest
ex. However, smoking may have confounded the association between alcohol and CHD. Smoking is a risk factor in its own right for CHD, so is independently associated with the outcome, and smoking is also associated with alcohol consumption because smokers tend to drink more than non-smokers.
what is attrition bias?
withdrawals or exclusions of people entered into a study
ex. in an intervention study of diet in people with depression, those with more severe depression might find it harder to adhere to the diet regimen and therefore more likely to leave the study
what is detection bias?
how outcomes are assessed
- Blinding (or masking) of outcome assessors may reduce the risk that knowledge of which intervention was received, rather than the intervention itself, affects outcome measurement.
ex. if providers in a psychotherapy trial are aware of the investigators’ hypotheses, this knowledge could unconsciously influence the way they rate participants’ progress.
