Evidenced Based Dentistry 1 Flashcards
what is the definition of risk
what are the chances
can be good or bad
what is the definition of outcome
something that might happen
what are statistics
numbers that summarize information
what are statistics based on
observations of large numbers of people
what are statistics useful for
predicting what is likely to happen in the future
what does the numerator represent
number of people who actually experience the outcome
what does the denominator represent
the number of people who could potentially experience the outcome
what are risks and odds
just ways of expressing chance in numbers
for binary events they just express the chance of being in one of the two states
how do you calculate risk
number of events of interest/total number of observations
how do you calculate odds
number of events of interest/number without the event
what are the questions to ask when interpreting risk
risk of what - what is the outcome?
how big is the risk - what are the chances of experiencing the outcome, what timeframe?
does the risk information reasonably apply to me or my patient?
how does this risk compare with others risks - should i do something about this risk
what are the questions to ask about risk reduction
reduced risk of what?
how big is the risk reduction?
does the risk reduction info reasonably apply to me?
any downsides?
is the benefit (risk reduction) worth the downsides?
what is the difference between the relative risk reduction and absolute risk reduction
relative risk reduction makes even small risk reductions sound big making us overestimate the benefits
what is the number needed to treat
the number of patients you would need to treat to prevent one patient from developing the disease/condition/outcome
what is a confidence interval
a confidence interval tells us the range of values that a true population treatment effect is likely t lie
describe what confidence intervals show
a CI that embraces/overlaps/contains/straddles the ‘value of no difference’ between treatments indicates that there is insufficient evidence for a difference between the treatment and control group in the population
what is the ratio value for confidence intervals
if the confidence interval embareces 1 then there is insufficient evidence
if this interval does not embrace 1 then there is sufficient evidence to suggest a difference
if two values are equal what is the value of no difference
0
there is sufficient evidence for a difference between two values in the population if the CI for the difference does not overlap 0
if two values are equal in a ratio what is the value of no difference
1
sufficient evidence for a difference between two values in the population if the CI for the ratio does not overlap 1
what are the different study designs in human research
observational uncontrolled studies
controlled studies
randomized controlled trials
what are observational uncontrolled studies
researchers watch what happens to a group of people
what are controlled studies
cohort or case control
researchers observe what happens to people in different situations without intervening
what are randomized controlled trials
patients randomly split into 2 groups - one gets intervention and the other placebo
any differenced at follow-up caused by intervention
what is a case report/case series
a report on a single patient or series of patients with an outcome of interest - no control group is involved
what is a case report/case study used for
identify the new disease outcome
hypothesis generation
what are the disadvantages of a case study
cannot demonstrate the valid statistical associations
lack of control group
what are cross sectional studies
the observation of a defined population at a single point in time - or time interval
exposure and outcome are determined at the same time
what are cross sectional studies used for
estimating prevalence of a disease
investigate potential risk factors
what are the disadvantages of cross sectional studies
causality
confounding
recall bias
what is a case control study
the study of people with a disease and a suitable control group of people without the disease
looks back in time at exposure to a particular risk factor in both groups
what is a case control study used for
looking at potential causes of disease
what are the disadvantages of case control study
confounding recall/selection bias selection of controls time relationships (did exposure occur before disease)
what is a cohort study
establish a group of individuals in population
measure exposures
follow up over a period of time
identify those that develop disease (outcome of interest)
what is a cohort study used for
estimating incidence of disease
investigating causes of disease
determining prognosis
timing and direction of events
what are disadvantages of cohort studies
controls difficult to identify confounding blinding difficult for rare diseases - need large samples very expensive/time consuming
what are randomized controlled trials
sometimes referred to as a clinical standard
considered the gold standard
for effectiveness and efficiency
particularly useful for clinical studies
provides strongest evidence on effectiveness of treatments
what are the 4 design elements of RCT
specification of participants (inclusion/exclusion criteria)
control/comparison groups
randomisation
blinding/masking
what are the inclusion/exclusion criteria
unambiguous
exact definitions
what is the comparison groups
placebo
current standard treatment
what is randomization
how participants/subjects/patients are allocated to treatments
why is randomization done
eliminate bias
how should randomization be done
by a computer
what is blinding/masking
if the participant or researcher is unaware of which treatment is given it may influence the results
what may change if participant/researcher is aware of which treatment is being given
participant
administrator of treatment
assessor of outcome
data analyst
what are the advantages of RCTs
provide strongest and most direct epidemiological evidence for causality
but non blinded RCTs may overestimate effects
what are disadvantages of RCTs
more difficult to design and conduct than observation studies due to ethical issues, feasibility, costs
still some risk of bias and generalizability often limited
not suitable for all research questions
