module 1 Flashcards
confidence interval interpretation
There is about a 95% probability that the true value of EGO in the whole population of interest, from which the study participants were recruited, lies between 8.0 and 10.0.
2 types of recruitment error
external validity error - when the Participants (P) who are recruited are not representative of the eligible population
non response bias - when a substantial proportion of the eligible population do not agree to take part
2 types of allocation error
confounding (not error or bias) - when the exposure and comparison groups differ by other factors - not just the study ‘exposure’ - which also have an effect on the study outcome, then it is not possible to know whether the study exposure or the other factors caused EGO
and CGO to differ.
measurement error (blind or objective) of exposures - occurs if
the exposure(s) and comparison exposures are measured incorrectly causing some participants to be incorrectly allocated to the wrong group.
4 types of random error
-The randomness inherent in biological phenomena
-Random allocation error
-Random measurement / assessment error
-Random sampling error
how to reduce confounding
one way is to allocate participants by a random process
The main alternative approach to randomly allocating participants to EG and CG is to
allocate participants by measurement
Stratified/adjusted analysis - by dividing participants into ‘strata’, equivalent to dividing the study participants in the triangle into two circles and then analysing the data as if there were two sub-studies
baseline comparison
In RCT, randomly
allocating participants may not produce groups with similar characteristics, just by chance
alone. Therefore it is always important to check for differences between EG and CG at the beginning of a study
Most preferable non-random error
Maintenance error will only result in outcomes that are underestimated and never overestimated.
solution for confounding in RCT
concealment of allocation - conceals the allocation decision from the participant and investigator
triangle key parts
-the open top of triangle
represents the setting in which the eligible population was recruited
-combining the two lower
levels, represents the eligible population
-the tip of the triangle represents those
from the eligible population who agree to take part
Random sampling error
Even if the recruitment process is done perfectly, the participants will never be a perfectly representative sample of the whole population because you would literally have to include every individual in the population
Random measurement/assessment error
Our ability to measure
biological factors in exactly the same way, every time we measure them, is often poor,
particularly if the measurement instrument requires a human operator
The randomness inherent in biological phenomena
The inherent variability in all biological phenomena and
therefore inherent variability in all measurements of biological phenomena
Random allocation error
Exposure and comparison groups in a randomised
controlled trial may differ by chance alone, particularly if the trial is small
relative risk statement
when RR >1
risk in EG is 2 times higher than than in CG
EG is 2 times as likely/100% more likely to … than CG
% calculated from RRI (RR-1)x100
extremal quotient formula and statement
highest rate/lowest rate = EQ
The highest ratio of (measles) incidence in EG was 8 times higher than the lowest rate of incidence in CG. This means EG are 8 times more likely (to contract measles) than CG
