systematic reviews and meta analysis course guide Flashcards
what is a systematic review
aims to answer defined question by collecting and summarising empirical evidence that fits eleigibility criteria
what is a meta analysis
statsistical techniques used in a systematic review to integrate the results of the studies
why do a systematic review
high volume of data
impossible for clinicians to analyse it all
individual studies - not enough power to make decisions
multiple studies = inconsistent results
review gives genrealisable conclusions
advantages to a systematic review
transparent - explicit methods
meta analysis increases power and enhance precision accounting for sample size and uncertainties
demonstrate lack of adequate evidence
stage 1 of the systematic review
plan
define the qn
frame qn around the participants, exposure, outcomes and study designs of interest
stage 2 of the systematic review
identify research - clearly defined search criteria and a thorough search of literature
selection of studies - inclusion and exclusion criteria a priori
study quality assessment - assessed against recognised/user defined criteria eg identify biases
stage 3
reporting and dissemination - details extracted and effect estimate
details tabulated
estimate an overall effect by combining the data
strength of meta analysis
more subjects - more reliable and precise estimate
heterogeneity can be identified and explored
weakness of meta analysis
if too heterogenous inappropriate to pool
stats and visualisation of meta analysis
forest plot
graphical representation of each result and combined meta analysis result
escribe publication bias
grewater likelihood of papers with stat significance to be published
failure to include all data (including null results) may mean effect is over/under represented
how is publication bias explored
funnel plots
see if link between study size and effect of estimate
heterogeneity exists because of
clinical, methodological differences and unknown study characteristics
how can studies differ
population, exposure, outcomes and designs used
how can you explore heterogeneity
Galbraith (radial) plots
limitations in systematic reviews
if too few studies matching criteria the review might not add much
if methods are inadequate - findings may be compromised
publication bias
guidelines and protocols for systematic review
Cochrane Database of Systematic reviews set standards. started to fascilitate the decisions people had to make for health interventions according to EBM
Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRIMSA) evidence based minimum set of items for reporting, focus on evaluating randomised controlled trials - bases for reporting systematic reviews - can be used for other things eg evaluation of interventions
prevalence
Number of cases of a disease within a defined population measured at a specific point in time. Prevalent cases include both new (incident) and existing cases.
how can HIV be tested for
self report
saliva and blood testing - ELISA
problem with measuring point prevalence
consider data available on census day - participation bias
problem with HIV tests
look at sensitivity and specificity
problem with self reporting
people might not know
or are ashamed
overall incidence =
new cases in cohort/total number in cohort
relative risk
incidence in exposed group/incidence in non-exposed group
what does relative risk of 8.14 mean
risk in exposed group >8x higher than non-exposed group
explanation for findings
chance bias representative/generalisable? confounding cause
should we circumcise men for HIV protection
yes - reduce rates and prevent spreading until vaccine is produced
no - not invulnerable, should only be used as part of wider strategy
summarise male circumcision for HIV prevention
reduce risk by 60%
3 randomised controlled trial shown circumcision with proper facilities is safe
only where there are heterosexual epidemics, high HIV and low male circumcision
should be combined with treatment for sexually transmitted infections; the promotion of safer sex practices; the provision of male and female condoms and promotion of their correct and consistent use.