midterm 1 Flashcards
what is the effect of the expectation on the result of the research
expectations can
dramatically distort our perceptions of
subjective measures
what are example of the expectation on our health and what we think about the others
If we expect to feel better, our perception
of pain can improve by 30% or more
* If we expect others to feel better, many
of us we will see imaginary
improvements
* Conversely, if we expect to feel worse, we
will often imagine deteriorations in
subjective measure
what factors increase the expectations
Factors that can increase expectations
include the novelty, mystique,
sophistication, or simplicity of the
intervention, and the confidence or
friendliness of the practitioner
what is the blinding
One of the most effective methods for
minimizing expectation bias is to
conceal the identity of the treatment
from both the participants and
researchers until the trial has ended
– this is known as blinding
what are the two steps factors in blinding
Two important steps in blinding are:
* Making the treatments as similar as possible in appearance, odour,
flavour, etc., so participants and researchers cannot tell them apart
* Replacing the treatment labels with codes
can blinding reduce the exaggeration
Blinding can markedly reduce exaggeration:
who should be blinded as possible
- Participants
- Healthcare providers
- Data collectors
(those who record symptoms, measure things like BP, administer surveys, etc.) - Outcome adjudicators
(those who decide if a participant has experienced the primary outcome) - Data analysts
do authors need to mention which group is blinded
Authors should explicitly state which groups are blinded instead of
using vague ‘single/double/triple-blind’ terminology
what we need to check to find that the research did the double blinding
1.The similarity of the treatments The treatments should be described in detail. You should be able to tell if they are sufficiently
similar to prevent people from figuring out who is receiving what
2. Who was blinded – are specific groups named, or is the description vague (e.g., ‘double-blind’)?
Look for mention of participants, treatment providers, etc.
3. If blinding was not possible or not done, check the outcome:.OK if the primary outcome is objective (e.g., a number, like mortality)
A fatal flaw is if it is subjective (e.g., a pain score, a survey) the unblinded study is useless
what are the unrelated reasons that somebody drop out of the research trial
Not everyone who enrols in a trial continues to participate until the end
Some stop participating for reasons unrelated to the treatment:
* They move away
* They develop a new medical condition that precludes ongoing participation
* They simply don’t want to bother
* etc.
what are some related reasons for dropping out of the research trial
Some drop out because of the treatment:
* They develop an adverse effect that they find intolerable
* In rare cases, a participant may die because of the intervention
what ignoring the dropped out people can cause distort the result
If those who drop out of a trial before it finishes are ignored, the results can become distorted in several ways:
1) Randomness can be lost, which can alter the results considerably
2) The sample size may become too small, resulting in an underpowered study
3) Severe adverse effects can be hidden
what is the per-protocol analysis
if we only included those who followed the entire protocol, this is called a ‘per protocol’ (PP) analysis
what is the intention to treat ITT analysis
if we included everyone who we
intended to treat, this is called an ‘intention-to-
treat’ (ITT) analysis
which analysis would CONSORT recommend ITT or PPT? why?
CONSORT recommends that an intention-to-
treat analysis always be presented, because it:
* maintains the random distribution of
confounding variables between groups
* maintains sample size & power
* is less likely to miss relevant adverse effects
why the PPT is not acceptable
a per-protocol analysis can:
* result in uneven losses of confounding
variables from the groups, biasing the
conclusions
* cause a loss of sample size & power, biasing
the conclusions
* conceal relevant adverse effects, since anyone who withdraws (or dies!) due to severe adverse effects are not taken into account
in what situation a PP is acceptable
PP is acceptable in addition to, but not instead
of, ITT
when the PP is appropriate
PP may be appropriate if there are few losses
and they are not related to the intervention
(e.g., pregnancy, moved away, etc.)
when the ITT is required
An ITT analysis is required if any of the following apply:
* Some participants died due to the treatment
* Some dropped out due to adverse effects of
the treatment
* Some left for unknown reasons
why do we need flow chart
To make it easier for the reader, CONSORT
recommends that all RCTs include a flow chart
showing how many people were randomized into each group, how many dropped out, and how many completed the trial
In addition, reasons for all losses should be
provided directly on the flow chart
what we need to check in the RCT to know which analysis was used
What to check in an RCT:
1. Look for a flow chart showing losses, with reasons.
If some losses are related to the intervention (adverse effects; deaths) or are ‘unknown’,
analysis should be ITT
2. Check the type of analysis
Check # in each group at beginning & end of trial which number was used in the analysis?
Has everyone been accounted for? (I.e., has an ITT analysis been performed?)
(Caution: Authors may wrongly call a per protocol analysis “modified ITT” or simply “ITT”)
3. Losses should be modest
Arbitrary rule of thumb: Concern if losses >10%
what does the assessing interpretation mean
Assessing ‘interpretation’ in an RCT means looking at the authors’ conclusions to see if they are justified by the data presented in the study
what are the three things that affect the interpretation of the data
1) Exaggeration
2) Surprising results
3) Limitations
explain the exaggeration
Exaggeration
As we have seen, exaggeration is common in the medical literature
It is therefore important to take a moment to check if the conclusions drawn by the authors are supported by the data presented in the RCT If they say they found an effect, look at the data to see if the groups were actually significantly different – sometimes they are not!
what is the Surprising results
If the authors find something that conflicts with what is known on a subject, the onus is on them to explain why we should believe their
results rather than the existing evidence
This is particularly important if the contradictory evidence is strong Therefore, the authors should provide a brief review of the existing
evidence, and comment on any apparent contradiction
what is study limitation
Study Limitations
CONSORT recommends that authors include a heading called “Limitations” to ensure that the reader is aware of the study’s weaknesses
The authors should explain how the limitations could have affected the results. in some cases no conclusions about efficacy can be drawn because of a severe deficiency Study authors sometimes describe weaknesses that are essentially fatal flaws, but then ignore them when drawing their conclusions The reader of an RCT should therefore look at the study’s limitations to see if
(1) they are easy to find, and (2) there are any weaknesses that render the
conclusions doubtful
what do we need to check to have a good interpretation of the data
Do the data in the tables and figures support the conclusions?
If the conclusions are not supported by the data, don’t accept them
Have the authors reviewed the existing evidence?
If their new findings are contradictory, the onus is on them to explain
why they are correct and previous researchers are wrong
Have the authors ignored serious limitations?
If the authors tell you of a serious flaw in their study that may make it impossible to draw any firm conclusions, they should take it into account when drawing their conclusions
what is CONSORT stand for
Consolidated Standards of
Reporting Trials
when CONSORT was published and when it was edited for the first time
Published 1996; substantial update
2001, minor edits 2010 (current
version)
what is the RCT is dicribing
The clarity with which an RCT is
described is known as ‘quality of
reporting’ (QOR)
what is the CONSORT and why do we need it in the RCT
CONSORT identifies 25 items that
should be clearly described in any RCT
Purpose is simply to allow the reader to
know what was done (whether the trial
was done well or poorly)
