Critical numbers Flashcards
What is a sample?
A selection from a population which aims to represent the whole population.
Name some types of bias and explain
Sampling bias, some people are more likely to be included in your sample than others. (omission, inclusive bias)
Recall bias, people cannot remember information correctly
Social- desirability bias, change answers to more acceptable ones
Information bias, errors in your measurements.
What is a confounding factor?
something that is related to the outcome and the characteristic of interest
What are the categories of studies?
– Experimental vs. Observational
– Retrospective vs. Prospective
– Individual vs. Population level
What is an experimental research method?
One where the researcher has made some kind of intervention eg crossover trial or RCT
What is an observational study?
There is no intervention data is just collected about what happens, E.g. case-control, cross-sectional,cohort,ecological studies
What is a retrospective study?
One which looks back at what has already happened case-control
What is a prospective study?
Collect information then follow up over time Cohort study
What is an individual study?
Collect information about individuals all studies except ecological.
What is a popilation study?
Talk about a whole population
What is the ecological fallacy
making inferences from populations about an individual.
Describe case-control studies
Find individuals with the outcome and a similar group without and take a random sample of each and see who had the eposure compared to others.
What are the strengths and weaknesses of case-control studies?
Strengths- good for rare diseases as sample can be focussed, quick results as its retrospective, can look at multiple causes, it is inexpensive.
Weaknesses- subject to recall bias, can’t prove causality, prone to selection and information bias, hard to choose controls, incidence of disease cannot be calculated
Describe a cross-sectional study
takes a snapshot of what is happening at the current time
What are the strengths and weaknesses of a cross-sectional study?
Strengths- quick to do, relatively cheap to generate hypotheses, few eithical problems
Weaknesses- could be a medical oddity, prone to sampling bisas no time reference
Describe a cohort study
Collect information on a sample and follow- up over time to explore who gets the outcome
What are the strengths and weaknesses of a cohort study?
They distiguich anecedent causes from concurrent associated factors. can calculate relative and absolute risks. can look at many outcomes or exposures less chance of bias as measured before disease onset/
Weaknesses- cannot be certain of causation, long study periods, follow up can be a problem, diagnosis of disease may change over time.
Describe a RCT?
Have multitple groups with different exposures compare the outcomes to get a causal relationship.
What are the strengths and weaknesses of an RCT?
Strengths- should equalise confounding factor effects, randomly allocating reduces bias blindign can be used, significance tests are better, the confounders and mabiases are minimised
Weaknesses need a big enough sample to show it works, volunteer bias can be a problem, ethical issues can be a problem for studies and poor compliance can lead to loss in power of the study.
What is a crossover trial?
an extension to an RCT. everyone does all the arms of the study. which reduces confounding even more as each person can be compared across the arms. thre can be carry-over effects and more technical analyses
What steps should be taken in an RCT to minimise bias?
Blinding, randomisation, placebos, matching
What are the two main groupings for variables?
Categoric and numeric
What are the types of categoric variables?
Binary, ordinal, nominal
what are the numeric variables?
Discrete and continuous
