what is a sample?
a group used to represent a population
what are the 5 types of sampling?
- random
- systematic
- quota
- cluster
- stratified
what is random sampling?
using a random number generator
what is systematic sampling?
every nth person is selected
what is quota sampling?
- convenience
- filling up a number
what is cluster sampling?
- divide people into groups (usually geographically)
- each group = cluster
- clusters randomly selected
what is stratified sampling?
- divide population into smaller groups (e.g. age)
- take a random sample of each
what are the types of bias involved in sampling?
- sampling bias
- recall bias
- social desirability
- confirmation bias
- volunteer bias
what is sampling bias?
non-representative sample
what is recall bias?
lack of specifics
what is social desirability?
lie about things for social reasons
what is confirmation bias?
interprets new evidence as confirmation of existing beliefs
what is volunteer bias?
volunteers unlikely to be representative
what are the types of bias involved in screening?
- selection bias
- lead-time bias
- length-time bias
what is selection bias?
participants selected are unlikely to be representative
what is lead-time bias?
overestimating the apparent time surviving with a disease by bringing forward the time of diagnosis
what is length-time bias?
overestimating the survival duration due to longer-living people being more likely to be picked up during screening
what are confounders?
- related to outcome and exposure
- may affect results so need to be taken into account
what is critical appraisal?
assessing reliability
- how consistent are the results of the study?
- is it repeatable?
assessing validity
- does the test investigate what it is meant to?
how would you generate a research question?
PICO P - patient of population (exposure) I - intervention C - control O - outcome
