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Science
Medicine
Public Health
EBP-Lecture 7
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Gravity
Terms in this set (70)
The term "Number Needed to Treat" refers to:
A. The number of treatment options available for a particular condition.
B. The number of patients who need to be treated during a given time frame in order to prevent one outcome. C. The number of patients who need to be treated within in a certain population to impact the disease prevalence.
D. The number of patients who need to be treated within a certain time frame within a certain population.
B
Which of the following study designs is considered the most ethical model to use when answering a harm question?
A. Randomized Controlled Trial
B. Systematic Review and Meta-analysis of a group of Randomized Controlled Trials
C. Case Control Study
D. Cross-over Study
C
The "5 to 20 Rule" refers to:
A. If a systematic review contains at least 5 individual studies, but no more than 20, then it is considered to be a valid review.
B. If less than 5% loss to follow up then not much bias introduced; If 20% or greater loss to follow up-serious threat to validity.
C. The Relative Risk Reduction is going to be 5% more than the Absolute Reduction 20% of the time.
D. Randomized Controlled trials report harm data 5% of the time while Case Control Studies report harm data 20% of the time.
B
ASK-->______-->_______--> ______-->_______
AQUIRE, APPRAISE, APPLY, AUDIT
What is a therapy Question?
Factors to consider? (6)
How to select appropriate and effective treatment/ intervention options for patients
Factors to consider are:
effectiveness,
safety,
side effects,
compliance,
cost,
accessibility, etc.
What IS THE MOST ACCURATE DESCRIPTION OF THE type of study that answers a therapy question?
intervention- a randomized controlled study
Randomized Clinical Trial
Random selection of groups that are balanced with respect to known and unknown determinants of outcome often answer a ______.
clinical question about therapy
Cohort vs.RCT
The individuals conducting the study identify the both the _____ & _______.
• Not as ______ but can be used in studying outcomes which are harmful or rare
• Exposed and unexposed groups may not have same risk for outcome
exposed cohort and the unexposed cohort
statistically valid
___- Random selection of groups that are balanced with respect to known and unknown determinants of outcome
• Less ____ & _____
• May take ____ to reveal meaningful data
(more expensive)
• Unethical in known harmful outcomes
RCT
bias& more valid
longer
Controlled vs. Observational
_____- Each element of the study is "controlled"
• Typically _____.
• Can be ____.
• Can draw conclusions regarding ____.
• Can pose a _____.
• Many confounding factors can be accounted for in this controlled environment
controlled
double blind
expensive
cause
moral dilema
____- is a factor that distorts the true relationship of the study variable of interest by virtue of also being related to the outcome of interest
cofounder (third variable)
OBSERVATIONAL
• Observing the effect of an exposure on those in the general population
• Not done in a ______.
• Can only draw conclusions regarding ___
• Can often be very large in number
• ______ are an issue
controlled
correlations
confounding factors
_______
Only relevant when the outcome is reversible (i.e.symptoms)
Requires a smaller sample size
Run in and Washout periods can be lengthy or unknown
Cross-Over Design
VALIDITY CRITERIA FOR A THERAPY STUDY
F= FOLLOW UP
R= RANDOMIZATION
I= INTENTION TO TREAT
S= SIMILAR AT BASELINE
B=BLINDING
E= EQUAL TREATMENT
Those lost to ______ create missing data that may disrupt the balance in groups created by randomization
Those who discontinue a study may have a different prognosis than that of those who continue
Follow-up
Why Randomize?
Minimizes
Maximizes
known and unknown baseline differences between groups
the likelihood that the intervention is the only systematic difference between the groups
• Form of randomization
• Ensures that the person who decides that a patient can enter the trial cannot influence the allocation at the time of study entry
• RCTs lacking a statement about allocation concealment are associated with larger effect‐size bias (33% if unclear, 41% if not done)
• Many RCTs do not adequately conceal allocation (done in 55% of RCTs in "best" journals, and only 7% of RCTs in "poorer" journals)
allocation concealment
ALLOCATION CONCEALMENT PLACE before______; AFTER ________
randomization
sequence generation
Subjects are analyzed in the group to which they were randomized, even if they discontinued their treatment or switched to another treatment
This is real life: patients don't always follow our advice
intention to treat
*Once Randomized Always Analyzed.
In regards to those lost to Follow up, if assuming a worst case scenario doesn't alter the inferences arising from the study results, then this decreases the ____ problem introduced by those lost
validity
_______
Analysis is limited to patients in which the treatment was completed according to plan
By restricting the analysis to a selected patient population, it does not show the practical value of the intervention
per protocol
______- is important for small trials in which treatment outcome may be affected by known clinical factors that have a large effect on prognosis
Once the decision to stratify is made, investigators need to chose factors carefully and account for them in the analysis
stratified randomization
Blinding maintains _________ between groups
______ prevents biased outcomes assessment
This becomes more important with subjective outcome
Who gets blinded?
prognostic balance
blinding
To prevent differential administration of therapies that affect outcome of interest (____)
co-interventions
_____- to prevent bias in decision about whether a patient has an outcome
adjunctors of outcomes
_____- to avoid bias in decisions around analysis
data analysis
_______- is the outcome of greatest importance
primary outcome
_______- are used to evaluate additional effects of the intervention
Data on secondary outcomes
______- are often physiological or biochemical
markers that can be relatively quickly and easily measured, and that are taken as being
predictive of important clinical outcomes
Measurement of BP making inferences regarding heart attack and stroke
surrogate outcomes
_____- consists of two or more component outcomes
• Patients who have experienced any one
of the events specified by the
components are considered to have
experienced this
• Can be misleading
composite outcome
A drug leads to a large
reduction in a composite outcome of "death or
difficulty breathing."
This could mean that the drug resulted in fewer deaths and less difficulty in breathing.
It also could be that the composite was driven entirely by a reduction in difficulty in breathing with no change, or even an increase, in death.
composite outcome
_____- Did the intervention/therapy effect have a statistically and clinically significant impact on
the diseases's natural history? (i.e. course of
the disease in left untreated)
measures of effect
Measures of Effect
• Relative Risk
• Relative Risk Reduction
• Absolute Risk Reduction
• Number Needed to Treat
• Number Needed to Harm
Absolute Risk Reduction is the most used clinically
_____- Rate of occurrence of an outcome or event in the treatment (intervention) group
Experimental Event Rate (EER)
______- Rate of occurrence of an outcome (event) in the control (notreatment/intervention) group
Control Event Rate (CER):
______- The percentage reduction in risk in the
treated group vs. the control group
relative risk
_____ if you hear:
relative
ratio
risk
divide
_____ if your hear:
Absolute
Difference
Reduction
subtract
______- percentage reduction in risk in the treated group compared to the reduction in risk in the control group
relative risk reduction
____- Proportion of baseline risk that is
removed by the intervention
Relative risk reduction
____- difference in risk in the intervention group and the control group in study
ARR-
_____- difference in risk expressed as a proportion
of the control event rate
RRR
_____- is often more "impressive" but less clinically useful than absolute risk reduction particularly
in low risk events
The _____ the event rate in the control group,
the larger the difference between relative risk
reduction and absolute risk reduction
Relative risk reduction
lower
The number of patients which must be treated during a specific time frame in order to prevent one outcome
The inverse of the ____ :
_______
# needed to treated
ARR
1/ARR
_____- presents data in a
positive light-as good rather than better
Non-inferiority trial:
________
Somewhere between these two points a
repeated measurement will lie 95% of the time (for a confidence interval with a 95% (or other)
confidence level)
confidence intervals
_____- Measure of the strength
of evidence of the null hypothesis of " no
effect"
In general, convention
takes < .05 as being statistically significant
p-value
CIs indicate both ____ & _____ of difference therefore they report both quantities of direct interest and the strength of the evidence
• _____ define the boundaries of the CI
• Many articles use both
size and direction
P values
Ascertaining the effects of potentially
harmful agents (including therapies) on patients
harm question
Harm can be studied in the
context of ______ simply by
measuring harms in addition to benefits-often
as secondary outcome measures
When outcomes are rare and/or studying them
would be unethical, other study designs are
frequently required
randomized control trials
Used to answer a questions regarding
harm Starts with a population having a
certain outcome
case control study
Requires small sample size, studies are done by
looking back in time, thus require little time to do (less expensive)
Susceptible to bias,
limited validity
Identification of a group of people who already have the outcome you are interested in studying
case control study
Useful in rare conditions
Useful when the required follow up is long
Draws weaker associations due to bias
case control studies
People with an adverse
outcome have a
different likelihood of
recalling an exposure
than those without the
outcome, independent
of the true extent of
exposure
recall bias
_____- the chance something occurs/the chances it could have occurred
risk( piece of pie compared to whole pie)
______- chance of it happening/chance of it not happening
odds ( piece of pie vs. What is left of pie )
When event rates are ____ and effect sizes are large, odds ratio and risk ratio
will be the _____
from one another
high
most different
RISK RATIO
RISK CANNOT BE MEASURED IN A
___________ BECAUSE THE
OUTCOME POPULATIONS ARE DEFINED BY THE
CONDUCTORS OF THE STUDY
case control study
How to estimate the patient's likely clinical
course over time and anticipate commonly
encountered complications of a particular disease or condition
prognosis question
______ can be identified if they have
different prognostic factors
Most valid when there is a pre-study that validates the power of the different prognostic
factor's impact on the outcome.
subgroups
Implicitly, RCT address issues of _______
• The control group results tells us information
regarding prognosis in those who did not receive the experimental treatment
• The experimental treatment group results gives us information regarding prognosis in those who did receive the investigational treatment
prognosis
This observational study design, whether or not it is done prospectively or retrospectively, always starts with an exposure
population
cohort
_______= {exposed cases with an outcome/total number of exposed cases}/
{outcomes in unexposed cases/total number
of unexposed cases}
RISK RATIO
_______= in a cohort study: odds of
outcome in exposed/odds ofoutcome in
unexposed
odds ratio
_____-Rate at which an outcome
happens
HAZARD
______- Hazard rate in the exposed group compared
to the hazard rate in the control group
Should accompany a measurement of ____
HAZARD RATIO.. Time
DEPICTED 1 OF 3 WAYS
Percentage of survival at a particular point in time
Median survival: length of follow up by which 50% of
study patients have died
For each point in time the proportion (expressed as a
percentage) of the original study sample who have
NOT yet had a specific outcome
survival curves
• The exposure and the outcome are measured
at the same time
• Provide a "snapshot" of the outcome and the
factors associated with it (one point in time)
• Limited value due to nature of design
• Can never draw causal conclusions based on
these studies
Cross-Sectional studies
• Can be used is assessing accuracy of a diagnostic
test
• Can estimate the prevalence of the outcome of
interest
• No loss to follow up
• Prevalence-incidence bias (also called Neyman
bias): Any risk factor that results in death will be
under-represented among those with the disease
cross sectional studies
Case control study(weaknesses)
A retrospective study. & true definition of inquiry is from outcome to exposure.
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