Transcript Knowledge Explosion

Knowledge
Why bother?
Alan, Gavin and Neil
Today’s Aims and
Objectives
• To initially make you feel a bit
uncomfortable
• To make you think and get your
brain’s cogs whirring
• To (hopefully!) leave you feeling
slightly better, and equipped with
some practical tips that will help you
in the exam, and your medical
Medicine is an ocean of
information
How do we keep ourselves from
drowning in the continuous flow
of information poured upon us
in the form of journals, papers,
textbooks, courses etc. ?
Discuss as a group – possible
strategies to keep updated
Some Practical Tips
•You don’t have to know
everything
•Limit yourself to a small number
of relevant journals e.g. BMJ and
BJGP
•Scan the contents, read the
abstracts/conclusions of papers,
then go back in more detail
later if necessary/relevant
Some Practical Tips
•Do little and often
•Try to set realistic goals
•Try to learn around patients –
easier to retain/recall info
•Sign up to GPnotebook tracker
(or similar) – keeps a record of
your learning – good for PDP
The truth, the whole
truth, and nothing but
the truth?
Dismantling the
misinformation in
research papers
Why do we need to appraise
research ourselves?
• Don’t believe what you are told by
anyone (including me)
– Spinning statistics is an industry
standard:
• Scientists do it to get papers published
• Governments do it to minimise expenditure
• Big Pharma does it to get you to prescribe their
drugs
• Its important to know what you need
to know
– Too much exists out there to read
everything
– Discarding the rubbish is an important
skill
Lies, damn lies and
Statistics
•You dont have to be able to do
statistics to read a paper
insightfully
•There are a few key questions to
ask about any research paper
– Why was it done?
– How was it done?
– What haven’t they told you?
– Do the results support the claims of
the authors?
Its all relative, innit?
• What does a Relative Risk mean? An
example
– Relative risk of coffee drinkers versus tea
drinkers acquiring vCJD =0.70 (95% CI 0.
68 - 0.72) (ref 1)
– In plain English, I estimate coffee
drinkers are 30% less likely to acquire
vCJD than tea drinkers.
– My margin of error in this estimate lies
between 24-30% less likely to acquire vCJD
(Im 95%
confident of this)
– How would NESCAFE spin this
Its absolutely nothing….
• It’s ABSOLUTE RISK what matters
– If risk of vCJD is 1 in 10 million for tea
drinkers, and 1 in 7 million for coffee
drinkers, would you really advocate every
patient switching to coffee?
– What if it was 1 in 10 tea drinkers, and 1
in 7 coffee drinkers?
– In both, the relative risk reduction is the
same (30%), but the absolute risk
reduction is very different
Absolute risk
• Coffee: 1 in 10 million
0.000000010
• Tea:
1 in 7 million
0.000000014
=
=
• The absolute risk reduction by
switching from tea to coffee is the
difference in rates = 0.000000004
• How can we translate this into a
meaningful figure for a patient to
Numbers needed to treat
(NNT)
• This is the most valuable tool you
have at your disposal for making
sense of statistics
• NNT = 1/absolute risk reduction
• In this example, it is the number of
patients you need to switch from
drinking tea to coffee to prevent 1
additional case of vCJD
NNT = 250,000,000 (or the whole US
vCJD reference
A multi-centre nested case-control
study of the effect of beverage
consumption on vCJD risk:
analysis from the NESCAFE cohort
study.
J. Swallow and P. Spitt (2006).
Swedish Journal of Epidemiology,
43 69-99.
Part 1 Take home
message
•Beware studies that sell their
message on relative risk
reductions or improvements
•Always try to determine what the
absolute risk difference is
•Convert this to NNT for a
meaningful value you can
explain to patients (or yourself)
Small group work
•Split into 4 groups
– ‘Pharmaceutical reps’
– ‘PCT pharmacy commissioners’
– ‘GPs’
– ‘Patients’ (this is the easy job!)
•Look at the abstract of this paper
on Clopidogrel versus Aspirin,
published in The Lancet, and
follow the briefing notes for each
group
You have 15 mins
•Work in groups to produce an
argument for your case, and
nominate a spokesperson to give
a brief talk to the patient
interest group.
•The patient group must then vote
to decide who gives the most
convincing argument, and state
what convinced them to vote
that way.
How did it turn out?
• The Drug reps will have pushed the
relative risk rather than absolute
risk, and side effect profile
• The PCT will have highlighted the cost
to prevent each additional MI (NNT)
and suggested patients should not
receive Plavix
• The GPs will have been caught in the
middle!
• The patients will have found it
difficult to see beyond their own
Notes from the full paper
• In most cases, there was no
significant difference in all cause
mortality between the two treatment
arms (not mentioned in abstract)
• The side effect profile is similar with
no differences
• The study was funded by the makers
of Plavix, and no conflict of interest
was stated
Critical appraisal
summary
• Consider the motives behind
presentation of results by the authors
• Ask yourself if the study ‘fits’ your
patients
• Ask yourself if there is a conflict of
interest
• Dont be frightened by high power
statistics – you should be able to ask
the same question of any trial – how
many patients do I have to treat, and
what is the cost to prevent one event.