Key words Flashcards
selection bias
systematic differences between baseline characteristics of the groups that are compared
- random sequence generation
- allocation concealment
performance bias
systematic differences between groups in the care that i provided, or in exposure to factors other than the interventions of interest
- blinding of participants and personnel
detection bias
systematic differences between groups in how outcomes are determined
- binding of outcome assessment
attrition bias
systematic differences between groups in withdrawals from a study
- incomplete outcome data
reporting bias
systematic differences between reported and unreported find gins
- selective outcome reporting: some outcomes have been measured by results not given
regression to the mean
extreme values partly due to chance
if repeated later, chances are they will be less extreme
this can give the appearance of improvement
- helped to avoid with placebo
equipoise
ethically we need to not know which treatment is better
contamination/crossover
participants randomised to the control group may unintentionally receive the intervention
intention to treat analysis
analyse according to the group they were originally allocated to
reduces allocation bias
may underestimate the effect
stopping/analyser bias
could choose to stop the trial early to give desired outcome
allocation concealment
when randomisation is undertaken the researchers should not know whether a participant will be allocated to the intervention or control arm
- this prevents researchers from influencing which participants are assigned to which group
Sample size: significance
at what significance level will we accept there is a difference
Sample size: power
how certain do we want to be to find a difference if there is one
incidence rate
number of new cases/number of person years accumulated
incidence risk
number of new cases/nmner of persons at risk at the beginning of the period
point prevelance
number of person with disease at some time point/ total population at risk at the same time point
period prevalence
number of persons with disease at any time during a specified period/total population seen over the period of time
What are the criteria for assessing causality?
- biological plausibility
- time
- strength of association
- dose response
- consistency
- specificity
- coherence
- experiments
spectrum bias
DTA’s specific groups of patients are inappropriately excluded e.g. difficult to diagnose patients
- test appears more accurate than it actually is
response/responder/participation bias
systematic error ue to difference in characteristic between those who choose to volunteer to participate and those who do not
healthy worker effect
the deficit of both morbidity and mortality when workers and the general population are compared
- workers are usually less ill
interviewer bias
interviewer influences data gathers
- might probe cases more compared to controls
recall bas
differences in accuracy of completeness of prior exposure between controls and cases
recording bias
error that arises due to the information of interest being systematically recorded in more detail by the cases than the crotnrl se.g. medical record or self completed questionnaires
social acceptability bias
selective suppression or revealing of info the treats to the exposure of interest, so that the most socially acceptable answer is given
- reduce my annonimised questionnaire
detection bias
systematic difference between groups in how outcomes are determined
- blinding of outcome assures may reduce the risk
performance bias
- differences between groups in the care that is provided
reporting bias
differences between reported and unreported findings
- within a report those analyses with stat significant differences are more likely to be reported
verification bias
systematic error in DTA’s that ares when not all the participants receive both the index test and reference standard
review bias
systematic error in DTA’s when the interpretation of index test and reference standard are not independent
reflexive stance of the researcher
in qualitative studies the explicit reflection of the researcher son how their background, professional role or personality influences their relationship with the participants, or interpretation of data, and thus affect their research
causality: temporality
exposure must precede its supposed effect
- best demonstrated in cohort studies
causality: strength
the stronger the association the more we are inclined to believe a causal relationship
causality: biological gradient
a cause-effect hypothesis is strengthened if the risk of developing the disease increases with the exposure
causality: consistency
similar results obtained from studies with different methodologies in different populations, place and times add considerable weight to the general cause-effect argument
causality: plausibility
if there is known biological medchanism
causality: coherence
what ever mechanism is proposed, it should not fundamentally contradict the present knobbly
causality: specificity
the supposed cause is associated with one dissed only o the disease is associated with one cause only
- rarely used nowadays
causality: analogy
a causal link is more likely if analogy exists with other disease, species and settings
e.g. thalidomide
iterative method
constant comparison of data throughout collection
interview, modify, interview, modify
repeating cycles of data collection and analysis until saturation is reached and no new themes emerge
Qualitative: transparency
explicitness of methods and analysis
Qualitative: validity
justify interpretation, possible return to participants/invite their comments
Qualitative: reliability
different researchers will analyse differently but using more than one coder can flag up blind spots andincerase complexity
Qualitative: comparative
compare between and within individuals participants accounts, compare with other studies
Qualitative: reflexivity
account for role of researcher
