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DVT risk and air travel
DVT risk and air travel
The only study that I can find that measures the effect of class of
travel on the chance of getting a DVT is this on (all the other
articles seem to refer back to it):
S Afr Med J. 2003 Jul;93(7):522-8.
The BEST study--a prospective study to compare business class versus
economy class air travel as a cause of thrombosis.
"
Only 434 subjects had a full venous duplex scan performed. None had
ultrasonic evidence of venous thrombosis. Nine passengers tested at
departure had elevated D-dimer levels and these volunteers were
excluded from further study. Seventy-four of the 899 passengers had
raised D-dimers on arrival. Twenty-two of 180 business class
passengers (12%) developed elevated D-dimers compared with 52 of 719
economy class passengers (7%). There was no significant association
between elevation of D-dimers and the class flown (odds ratio (OR)
0.61, p = 0.109).
"
I'd imagine that a huge amount of money, potentially, rests on this
evidence, so I'm surprised that this is the only study. I haven't got
Dr Jacobson's e-mail address at Wits, nor the whole text of the study
yet, but I'll follow these up to understand more detail and if there
was any special funding.
I find something curious about the above, though, maybe somebody with
some knowledge of statistics can help explain it.
1. If all air passengers were the same, and there was no bias caused
by the class of travel, then you'd expect, I'd have thought, to find
the same raised D-dimers (the proxy for potential DVT in the study) in
both populations. To me, finding 14% in on population and 7% in the
other would suggest that the first population was twice as likely to
suffer the effect.
2. Clearly the size of study is important. So, though the whole study
includes nearly 900 passengers, the study only examines 180 business
class passengers. So, these are less likely to be representative than
those not in business class.
3. Isn't it also likely that those flying in Business class will have
other characteristics that differ that might be significant in their
risk of DVT? Shouldn't these factors be exluded before a comparison is
made?
4. How, then, do they come to the conclusion that there is no effect?
A simple minded reading of the conclusion suggests to me that Business
Class might be more dangerous. However, if Business Class passengers
are older, fatter and maler than economy class passengers, all of
these being predisposing factors (some might even have been in
Business Class specifically because they were higher risk passengers
for other reasons) might, when excluded, show that Business Class is,
in fact, much safer.
How can this 2003 study be the only thing on which we can base our
conclusions?
Is it possible that airlines have tested this themselves (I'd find it
odd if this had not occurred to any airline) and decided not to
publish the results?
After all, if business class was much safer, then there would be
considerable pressure to increase the space in economy, rather than
put these passengers at a health risk - the conclusion of the study
removes this pressure. Alternatively, if it is actually the case that
business class is more dangerous, then fewer people would pay three
times the price for it - at least on health grounds.
The only study that I can find that measures the effect of class of
travel on the chance of getting a DVT is this on (all the other
articles seem to refer back to it):
S Afr Med J. 2003 Jul;93(7):522-8.
The BEST study--a prospective study to compare business class versus
economy class air travel as a cause of thrombosis.
"
Only 434 subjects had a full venous duplex scan performed. None had
ultrasonic evidence of venous thrombosis. Nine passengers tested at
departure had elevated D-dimer levels and these volunteers were
excluded from further study. Seventy-four of the 899 passengers had
raised D-dimers on arrival. Twenty-two of 180 business class
passengers (12%) developed elevated D-dimers compared with 52 of 719
economy class passengers (7%). There was no significant association
between elevation of D-dimers and the class flown (odds ratio (OR)
0.61, p = 0.109).
"
I'd imagine that a huge amount of money, potentially, rests on this
evidence, so I'm surprised that this is the only study. I haven't got
Dr Jacobson's e-mail address at Wits, nor the whole text of the study
yet, but I'll follow these up to understand more detail and if there
was any special funding.
I find something curious about the above, though, maybe somebody with
some knowledge of statistics can help explain it.
1. If all air passengers were the same, and there was no bias caused
by the class of travel, then you'd expect, I'd have thought, to find
the same raised D-dimers (the proxy for potential DVT in the study) in
both populations. To me, finding 14% in on population and 7% in the
other would suggest that the first population was twice as likely to
suffer the effect.
2. Clearly the size of study is important. So, though the whole study
includes nearly 900 passengers, the study only examines 180 business
class passengers. So, these are less likely to be representative than
those not in business class.
3. Isn't it also likely that those flying in Business class will have
other characteristics that differ that might be significant in their
risk of DVT? Shouldn't these factors be exluded before a comparison is
made?
4. How, then, do they come to the conclusion that there is no effect?
A simple minded reading of the conclusion suggests to me that Business
Class might be more dangerous. However, if Business Class passengers
are older, fatter and maler than economy class passengers, all of
these being predisposing factors (some might even have been in
Business Class specifically because they were higher risk passengers
for other reasons) might, when excluded, show that Business Class is,
in fact, much safer.
How can this 2003 study be the only thing on which we can base our
conclusions?
Is it possible that airlines have tested this themselves (I'd find it
odd if this had not occurred to any airline) and decided not to
publish the results?
After all, if business class was much safer, then there would be
considerable pressure to increase the space in economy, rather than
put these passengers at a health risk - the conclusion of the study
removes this pressure. Alternatively, if it is actually the case that
business class is more dangerous, then fewer people would pay three
times the price for it - at least on health grounds.
Reply from: -- messaggio eliminato --
Date: 21 May 2008, 09:24
-- deleted messages --
Re: DVT risk and air travel
"Peter Brooks" <Peter.H.M.Brooks@gmail,com > wrote in message
news:f26bce74-9036-46dd-9460-6ac9fb20b16d@a9g2000prl.googlegroups,com ...
> The only study that I can find that measures the effect of class of
> travel on the chance of getting a DVT is this on (all the other
> articles seem to refer back to it):
>
> S Afr Med J. 2003 Jul;93(7):522-8.
> The BEST study--a prospective study to compare business class versus
> economy class air travel as a cause of thrombosis.
>
> "
> Only 434 subjects had a full venous duplex scan performed. None had
> ultrasonic evidence of venous thrombosis. Nine passengers tested at
> departure had elevated D-dimer levels and these volunteers were
> excluded from further study. Seventy-four of the 899 passengers had
> raised D-dimers on arrival. Twenty-two of 180 business class
> passengers (12%) developed elevated D-dimers compared with 52 of 719
> economy class passengers (7%). There was no significant association
> between elevation of D-dimers and the class flown (odds ratio (OR)
> 0.61, p = 0.109).
> "
>
> I'd imagine that a huge amount of money, potentially, rests on this
> evidence, so I'm surprised that this is the only study. I haven't got
> Dr Jacobson's e-mail address at Wits, nor the whole text of the study
> yet, but I'll follow these up to understand more detail and if there
> was any special funding.
>
> I find something curious about the above, though, maybe somebody with
> some knowledge of statistics can help explain it.
>
> 1. If all air passengers were the same, and there was no bias caused
> by the class of travel, then you'd expect, I'd have thought, to find
> the same raised D-dimers (the proxy for potential DVT in the study) in
> both populations. To me, finding 14% in on population and 7% in the
> other would suggest that the first population was twice as likely to
> suffer the effect.
>
> 2. Clearly the size of study is important. So, though the whole study
> includes nearly 900 passengers, the study only examines 180 business
> class passengers. So, these are less likely to be representative than
> those not in business class.
>
> 3. Isn't it also likely that those flying in Business class will have
> other characteristics that differ that might be significant in their
> risk of DVT? Shouldn't these factors be exluded before a comparison is
> made?
>
> 4. How, then, do they come to the conclusion that there is no effect?
Their conclusion is "There was no significant association between elevation
of D-dimers and the class flown (odds ratio (OR)> 0.61, p = 0.109)", which
means that, according to their calculations, the probability of the apparent
association being due to nothing more than chance is 10.9%; by convention, a
result is only regarded as statistically significant if this probability is
less than 5%.
It is not clear to me how they reached this conclusion. According to the
figures given, the odds for business class passengers to have raised
D-dimers on arrival were found to be 22/158 and for economy class passengers
52/667. The ratio between these is 1.79 or 0.56, depending on which way
round you take them, and calculating the 95% confidence intervals as
described, for example, here
http :// www .bmj,com /cgi/content/full/320/7247/1468 , gives intervals of
1.05-3.03 and 0.33-0.95 respectively. Since these intervals do not include
the value 1, that seems to indicate p < 0.05. Does the full text of the
study give any more information on how they arrived at their stated figures
for the odds ratio and p?
"Peter Brooks" <Peter.H.M.Brooks@gmail,com > wrote in message
news:f26bce74-9036-46dd-9460-6ac9fb20b16d@a9g2000prl.googlegroups,com ...
> The only study that I can find that measures the effect of class of
> travel on the chance of getting a DVT is this on (all the other
> articles seem to refer back to it):
>
> S Afr Med J. 2003 Jul;93(7):522-8.
> The BEST study--a prospective study to compare business class versus
> economy class air travel as a cause of thrombosis.
>
> "
> Only 434 subjects had a full venous duplex scan performed. None had
> ultrasonic evidence of venous thrombosis. Nine passengers tested at
> departure had elevated D-dimer levels and these volunteers were
> excluded from further study. Seventy-four of the 899 passengers had
> raised D-dimers on arrival. Twenty-two of 180 business class
> passengers (12%) developed elevated D-dimers compared with 52 of 719
> economy class passengers (7%). There was no significant association
> between elevation of D-dimers and the class flown (odds ratio (OR)
> 0.61, p = 0.109).
> "
>
> I'd imagine that a huge amount of money, potentially, rests on this
> evidence, so I'm surprised that this is the only study. I haven't got
> Dr Jacobson's e-mail address at Wits, nor the whole text of the study
> yet, but I'll follow these up to understand more detail and if there
> was any special funding.
>
> I find something curious about the above, though, maybe somebody with
> some knowledge of statistics can help explain it.
>
> 1. If all air passengers were the same, and there was no bias caused
> by the class of travel, then you'd expect, I'd have thought, to find
> the same raised D-dimers (the proxy for potential DVT in the study) in
> both populations. To me, finding 14% in on population and 7% in the
> other would suggest that the first population was twice as likely to
> suffer the effect.
>
> 2. Clearly the size of study is important. So, though the whole study
> includes nearly 900 passengers, the study only examines 180 business
> class passengers. So, these are less likely to be representative than
> those not in business class.
>
> 3. Isn't it also likely that those flying in Business class will have
> other characteristics that differ that might be significant in their
> risk of DVT? Shouldn't these factors be exluded before a comparison is
> made?
>
> 4. How, then, do they come to the conclusion that there is no effect?
Their conclusion is "There was no significant association between elevation
of D-dimers and the class flown (odds ratio (OR)> 0.61, p = 0.109)", which
means that, according to their calculations, the probability of the apparent
association being due to nothing more than chance is 10.9%; by convention, a
result is only regarded as statistically significant if this probability is
less than 5%.
It is not clear to me how they reached this conclusion. According to the
figures given, the odds for business class passengers to have raised
D-dimers on arrival were found to be 22/158 and for economy class passengers
52/667. The ratio between these is 1.79 or 0.56, depending on which way
round you take them, and calculating the 95% confidence intervals as
described, for example, here
http :// www .bmj,com /cgi/content/full/320/7247/1468 , gives intervals of
1.05-3.03 and 0.33-0.95 respectively. Since these intervals do not include
the value 1, that seems to indicate p < 0.05. Does the full text of the
study give any more information on how they arrived at their stated figures
for the odds ratio and p?
Re: DVT risk and air travel
On May 25, 1:55 am, "Philip" <pp...@tiscali.co.uk> wrote:
> "Peter Brooks" <Peter.H.M.Bro...@gmail,com > wrote in message
>
> news:f26bce74-9036-46dd-9460-6ac9fb20b16d@a9g2000prl.googlegroups,com ...
>
>
>
> > The only study that I can find that measures the effect of class of
> > travel on the chance of getting a DVT is this on (all the other
> > articles seem to refer back to it):
>
> > S Afr Med J. 2003 Jul;93(7):522-8.
> > The BEST study--a prospective study to compare business class versus
> > economy class air travel as a cause of thrombosis.
>
> > "
> > Only 434 subjects had a full venous duplex scan performed. None had
> > ultrasonic evidence of venous thrombosis. Nine passengers tested at
> > departure had elevated D-dimer levels and these volunteers were
> > excluded from further study. Seventy-four of the 899 passengers had
> > raised D-dimers on arrival. Twenty-two of 180 business class
> > passengers (12%) developed elevated D-dimers compared with 52 of 719
> > economy class passengers (7%). There was no significant association
> > between elevation of D-dimers and the class flown (odds ratio (OR)
> > 0.61, p = 0.109).
> > "
>
> > I'd imagine that a huge amount of money, potentially, rests on this
> > evidence, so I'm surprised that this is the only study. I haven't got
> > Dr Jacobson's e-mail address at Wits, nor the whole text of the study
> > yet, but I'll follow these up to understand more detail and if there
> > was any special funding.
>
> > I find something curious about the above, though, maybe somebody with
> > some knowledge of statistics can help explain it.
>
> > 1. If all air passengers were the same, and there was no bias caused
> > by the class of travel, then you'd expect, I'd have thought, to find
> > the same raised D-dimers (the proxy for potential DVT in the study) in
> > both populations. To me, finding 14% in on population and 7% in the
> > other would suggest that the first population was twice as likely to
> > suffer the effect.
>
> > 2. Clearly the size of study is important. So, though the whole study
> > includes nearly 900 passengers, the study only examines 180 business
> > class passengers. So, these are less likely to be representative than
> > those not in business class.
>
> > 3. Isn't it also likely that those flying in Business class will have
> > other characteristics that differ that might be significant in their
> > risk of DVT? Shouldn't these factors be exluded before a comparison is
> > made?
>
> > 4. How, then, do they come to the conclusion that there is no effect?
>
> Their conclusion is "There was no significant association between elevation
> of D-dimers and the class flown (odds ratio (OR)> 0.61, p = 0.109)", which
> means that, according to their calculations, the probability of the apparent
> association being due to nothing more than chance is 10.9%; by convention, a
> result is only regarded as statistically significant if this probability is
> less than 5%.
>
> It is not clear to me how they reached this conclusion. According to the
> figures given, the odds for business class passengers to have raised
> D-dimers on arrival were found to be 22/158 and for economy class passengers
> 52/667. The ratio between these is 1.79 or 0.56, depending on which way
> round you take them, and calculating the 95% confidence intervals as
> described, for example, here http :// www .bmj,com /cgi/content/full/320/7247/1468, gives intervals of
> 1.05-3.03 and 0.33-0.95 respectively. Since these intervals do not include
> the value 1, that seems to indicate p < 0.05. Does the full text of the
> study give any more information on how they arrived at their stated figures
> for the odds ratio and p?
>
No, it doesn't, it simply declares that it is not significant.
On May 25, 1:55 am, "Philip" <pp...@tiscali.co.uk> wrote:
> "Peter Brooks" <Peter.H.M.Bro...@gmail,com > wrote in message
>
> news:f26bce74-9036-46dd-9460-6ac9fb20b16d@a9g2000prl.googlegroups,com ...
>
>
>
> > The only study that I can find that measures the effect of class of
> > travel on the chance of getting a DVT is this on (all the other
> > articles seem to refer back to it):
>
> > S Afr Med J. 2003 Jul;93(7):522-8.
> > The BEST study--a prospective study to compare business class versus
> > economy class air travel as a cause of thrombosis.
>
> > "
> > Only 434 subjects had a full venous duplex scan performed. None had
> > ultrasonic evidence of venous thrombosis. Nine passengers tested at
> > departure had elevated D-dimer levels and these volunteers were
> > excluded from further study. Seventy-four of the 899 passengers had
> > raised D-dimers on arrival. Twenty-two of 180 business class
> > passengers (12%) developed elevated D-dimers compared with 52 of 719
> > economy class passengers (7%). There was no significant association
> > between elevation of D-dimers and the class flown (odds ratio (OR)
> > 0.61, p = 0.109).
> > "
>
> > I'd imagine that a huge amount of money, potentially, rests on this
> > evidence, so I'm surprised that this is the only study. I haven't got
> > Dr Jacobson's e-mail address at Wits, nor the whole text of the study
> > yet, but I'll follow these up to understand more detail and if there
> > was any special funding.
>
> > I find something curious about the above, though, maybe somebody with
> > some knowledge of statistics can help explain it.
>
> > 1. If all air passengers were the same, and there was no bias caused
> > by the class of travel, then you'd expect, I'd have thought, to find
> > the same raised D-dimers (the proxy for potential DVT in the study) in
> > both populations. To me, finding 14% in on population and 7% in the
> > other would suggest that the first population was twice as likely to
> > suffer the effect.
>
> > 2. Clearly the size of study is important. So, though the whole study
> > includes nearly 900 passengers, the study only examines 180 business
> > class passengers. So, these are less likely to be representative than
> > those not in business class.
>
> > 3. Isn't it also likely that those flying in Business class will have
> > other characteristics that differ that might be significant in their
> > risk of DVT? Shouldn't these factors be exluded before a comparison is
> > made?
>
> > 4. How, then, do they come to the conclusion that there is no effect?
>
> Their conclusion is "There was no significant association between elevation
> of D-dimers and the class flown (odds ratio (OR)> 0.61, p = 0.109)", which
> means that, according to their calculations, the probability of the apparent
> association being due to nothing more than chance is 10.9%; by convention, a
> result is only regarded as statistically significant if this probability is
> less than 5%.
>
> It is not clear to me how they reached this conclusion. According to the
> figures given, the odds for business class passengers to have raised
> D-dimers on arrival were found to be 22/158 and for economy class passengers
> 52/667. The ratio between these is 1.79 or 0.56, depending on which way
> round you take them, and calculating the 95% confidence intervals as
> described, for example, here http :// www .bmj,com /cgi/content/full/320/7247/1468, gives intervals of
> 1.05-3.03 and 0.33-0.95 respectively. Since these intervals do not include
> the value 1, that seems to indicate p < 0.05. Does the full text of the
> study give any more information on how they arrived at their stated figures
> for the odds ratio and p?
>
No, it doesn't, it simply declares that it is not significant.
Reply from: -- messaggio eliminato --
Date: 26 May 2008, 20:39
-- deleted messages --
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Date: 26 May 2008, 21:41
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Date: 26 May 2008, 21:57
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Date: 29 May 2008, 02:56
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Date: 29 May 2008, 05:48
-- deleted messages --
Reply from: -- messaggio eliminato --
Date: 29 May 2008, 10:38
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Reply from: -- messaggio eliminato --
Date: 29 May 2008, 12:20
-- deleted messages --
Reply from: -- messaggio eliminato --
Date: 31 May 2008, 16:46
-- deleted messages --
Reply from: -- messaggio eliminato --
Date: 31 May 2008, 16:59
-- deleted messages --
Re: DVT risk and air travel
On May 31, 4:46 pm, "ironjust...@aol,com " <ironjust...@aol,com > wrote:
> On May 29, 3:20 am, Peter Brooks <Peter.H.M.Bro...@gmail,com >
> wrote:smoking, for example, doesn't affect your risk of venous
> thrombosis, <<
>
> That doesn't seem right.
> Logic tells this is wrong.
> Cigarette smoking causes polycythemia / hyperviscosity and
> hyperviscosity / polycythemia and thrombosis are linked / higher rate
> of thrombosis.
>
Thrombosis, yes, but not venous thrombosis, arterial thrombosis.
On May 31, 4:46 pm, "ironjust...@aol,com " <ironjust...@aol,com > wrote:
> On May 29, 3:20 am, Peter Brooks <Peter.H.M.Bro...@gmail,com >
> wrote:smoking, for example, doesn't affect your risk of venous
> thrombosis, <<
>
> That doesn't seem right.
> Logic tells this is wrong.
> Cigarette smoking causes polycythemia / hyperviscosity and
> hyperviscosity / polycythemia and thrombosis are linked / higher rate
> of thrombosis.
>
Thrombosis, yes, but not venous thrombosis, arterial thrombosis.
Re: DVT risk and air travel
On May 31, 8:11 am, Peter Brooks <Peter.H.M.Bro...@gmail,com >
wrote:Thrombosis, yes, but not venous thrombosis, arterial thrombosis.
<<
These guys seem to show the treatment of polycythemia leads to a
decrease in venous thrombosis ..
http :// doctor.medscape,com /viewarticle/496544
Furthermore, in the only randomized controlled clinical trial to date,
in patients older than age 60 years, hydroxyurea was found to be more
effective than aspirin in preventing transient ischemic attacks,
digital microvascular ischemia, and venous thrombosis.[30]
These data indicate that idiopathic erythrocytosis is not rare and
that phlebotomy alone is both necessary and sufficient to prevent
thrombosis in such patients.
Who loves ya.
Tom
Jesus Was A Vegetarian!
http :// jesuswasavegetarian.7h,com
Man Is A Herbivore!
http :// tinyurl,com /a3cc3
DEAD PEOPLE WALKING
http :// tinyurl,com /zk9fk
> On May 31, 4:46 pm, "ironjust...@aol,com " <ironjust...@aol,com > wrote:> On May 29, 3:20 am, Peter Brooks <Peter.H.M.Bro...@gmail,com >
> > wrote:smoking, for example, doesn't affect your risk of venous
> > thrombosis, <<
>
> > That doesn't seem right.
> > Logic tells this is wrong.
> > Cigarette smoking causes polycythemia / hyperviscosity and
> > hyperviscosity / polycythemia and thrombosis are linked / higher rate
> > of thrombosis.
>
>
On May 31, 8:11 am, Peter Brooks <Peter.H.M.Bro...@gmail,com >
wrote:Thrombosis, yes, but not venous thrombosis, arterial thrombosis.
<<
These guys seem to show the treatment of polycythemia leads to a
decrease in venous thrombosis ..
http :// doctor.medscape,com /viewarticle/496544
Furthermore, in the only randomized controlled clinical trial to date,
in patients older than age 60 years, hydroxyurea was found to be more
effective than aspirin in preventing transient ischemic attacks,
digital microvascular ischemia, and venous thrombosis.[30]
These data indicate that idiopathic erythrocytosis is not rare and
that phlebotomy alone is both necessary and sufficient to prevent
thrombosis in such patients.
Who loves ya.
Tom
Jesus Was A Vegetarian!
http :// jesuswasavegetarian.7h,com
Man Is A Herbivore!
http :// tinyurl,com /a3cc3
DEAD PEOPLE WALKING
http :// tinyurl,com /zk9fk
> On May 31, 4:46 pm, "ironjust...@aol,com " <ironjust...@aol,com > wrote:> On May 29, 3:20 am, Peter Brooks <Peter.H.M.Bro...@gmail,com >
> > wrote:smoking, for example, doesn't affect your risk of venous
> > thrombosis, <<
>
> > That doesn't seem right.
> > Logic tells this is wrong.
> > Cigarette smoking causes polycythemia / hyperviscosity and
> > hyperviscosity / polycythemia and thrombosis are linked / higher rate
> > of thrombosis.
>
>
