From: altar@beaufort.sfu.ca (Ted Wayn Altar)
Newsgroups: rec.food.veg
Subject: Estimating Risk and Reductions in Risk
Date: 7 Apr 92 09:38:31 GMT
Organization: Simon Fraser University, Burnaby, B.C., Canada

=================================================================
|                                                               |
|  Here are some upper estimates by how much you can reduce     |
|  your risk of heart disease if you reduce your consumption of |
|  meat, dairy products and eggs by a given amount:             |
|                                                               |
|  10% reduction of consumption  =  9% reduction in risk        |
|  50%     "     "      "        =  45%    "      "  "          |
| 100%     "     "      "        =  90%    "      "  "          |
|                                                               |
|================================================================
(references below)
 
 
 The health benefits of vegetarianism is really beyond dispute.
With respect to the consumption of animals, less is better and
none is probably best.  Notwithstanding the evidence that
supports this extrapolation, we still have endless quibbles that
maybe just a little meat is still OK.  All this is very
reminiscent of our inveterate smoker who believes that maybe just
1 cigarette per day is still OK.  One can only wonder what might
be the sociological and psychological conditions behind people's
irrational persistence in denying the objective evidence that has
been around for decades.
 
 What most astonishes me is the apparent inconsequentiality of
ANY type of data generation on this issue (as well as many
others, for that matter).  We could cite ad nauseam the evidence,
all of which supports rather than contradicts, the extrapolation
that "none is best".  For the individual who wants to play it
safe with respect to her or his health, then indeed the best
advice is simply, "none is best".
 
 Isn't it remarkable that intelligent people who happen to still
be smokers will still deny in some manner the hazards incurred by
smoking.  (Some wit once remarked that a smoker is a person who
claims that `the more they fume the less they fret').  
What we have here, I think, is a very important social-
psychological problem.  One obvious factor is simply our own
tendencies towards a self-justificatory denial or convenient
inattention to the facts that contradict one's current dietary
practices.  Such psychological defense is common enough that we
don't need to be reminded of it here.  But curiously, even
vegetarians seem to underestimate the benefits of their diet.
 
 Permit me to suggest that part the problem may also be due to
our built-in resistance or inability to understand statistical
information.  For example, I am continuously astounded by the
sloppy and simply incorrect reportage of even the most elementary
statistics by the media.  Every time they will say with complete
certitude that party X is AHEAD of party Y in popular support
even though the difference in percentage points might be less
than the standard error of measurement!  People do seem to be
woefully inept at understanding statistical information and what
can be properly inferred from empirical data.
 
 Even when the facts seem correctly in hand, they still are
simply neglected.  It is as if Mark Twain's quip was being taken
literally,  "get your facts first, and then you can distort
'em as much as you please".
 
 There is some very interesting social-psychological research 
(e.g., Kahneman & Tversky, 1872 & 1984; Slovic et al., 1976)
that has some bearing on this matter.  Given that some readers
may not already familiar with it, I'll summarize a few findings
for general interest.  But first, to help illustrate what might
be our problem in assessing the data on risk, here are 
five questions to try out beforehand:
 
 
|================================================================|
|                                                                |
|  (1). Of the pairs of following hazards,                       |
|          which causes more deaths?                             |
|                                                                |
| breast cancer   or  diabetes                              1    |
| lung cancer     "   stomach cancer                        1    |
| all accidents   "   strokes                               2    |
| pregnancy       "   appendicitis                          2    |
| car accident    "   cancer of digestive system            2    |
| drowning        "   leukemia                              2    |
| electrocution   "   asthma                                2    |
| homicides       "   diabetes                              2    |
| botulism        "   small pock vaccinations               4    |
| tornados        "   excess cold                           4    |
| lightening      "   appendix                              8    |
| all accidents   "   all diseases                          16   |
| tornado         "   asthma                                21   |
| botulism        "   lightning                             52   |
| botulism        "   emphysema                          10,600  |
|                                                                |
|  (2) Which is more frequent:                                   |
|     Words starting with K or words with K as the 3rd letter?   |
|                                                                |
|  (3) Which is more probable:  To find 60 boys in a random      |
|     sample of 100 babies or to find 600 boys in a sample       |
|     of 1000 babies?                                            |
|                                                                |
|  (4) which birth order or sequence of  boy/girl births is      |
|     more likely to occur:   BBBGGG or GBBGBG ?                 |
|                                                                |
|  (5) If some money is to be spent on making more safe an       |
|     already reasonably safe 2-way highway, where do you        |
|     think it should be spent:                                  |
|       (a) lengthening acceleration/deacceleration lanes        |
|       (b) more street lights at intersections                  |
|       (c) cement crash barriers on the central divide.         |
|                                                                |
|              (For Answers: see below, but first write          |
|                      down your answers)                        |   
|================================================================|
 
 
A.  COGNITIVE TENDENCY TOWARDS A LEVELING OF RISK
 
In general, people over-estimate low probabilities of risk and
under- estimate high ones.  E.g., death due to botulism or being
caught in a tornado (rare hazards) are estimated by people to be
some 10 or even 100 times more frequent than they are.
Conversely, heart disease, cancer, & stroke, which are the
leading causes of death, are under-estimated by a factor of at
least 10.  As mental statisticians, we are prone to a kind of
irrepressible `regression towards the mean'.  Risk for cancer is
fast approaching 1 in 3 for the general population, but most
people think that their personal risk is far smaller.  Well, it
can't be smaller for everybody.  The single biggest reduction of
an individual's risk for cancer, and heart disease, is achieved by
a lacto-ovo vegetarian diet.  A vegan diet gives an even a much
greater reduction.
 
 
B.  AVAILABILITY HEURISTIC
 
    For hazards of roughly the same objective risk, some causes
are given far higher estimates than others.  Death from tornadoes
is judged to be much higher than death from vaccination.  The
answer to question (1) above is that everything in the second
column is the more likely event (numbers in the far right column
are the true ratios of the most likely event over the less
likely).  This distortion can be partly be attributed to the
dramatic and more publicized nature of some causes in the press
or TV. Other causes, like a meat-eating diet, are under-reported
and inconspicuous.  Indeed, people's estimated frequency of
certain causes of death correlates about .70 with the amount of
coverage for those kinds of deaths reported in newspapers.  The
"heuristic" or rule-of-thumb that people might be pre-
reflectively employing could go something like this:
 
     "Since frequently occurring events are easier to imagine or
     recall, then when in doubt, treat more readily recalled or
     imagined things as more frequent".
 
Hence, in problem (2) there are more words with K as the 3rd
letter but we find it easier to think of words with K as the
first letter.  Incidentally, even medical doctors, while more
accurate than non-experts, still are influenced by things like
the number of encounters they might have had with particular
death-causing diseases in the last year, over-rating the
probability of those things they just happened to have seen
personally.
 
 
C.   REPRESENTATIVENESS HEURISTIC
 
   Here people will tend to judge the likelihood of things in
terms of how well they represent what they think is a "typical"
occurrence of such things.  For example, there is the `gambler's
fallacy' where people think that because of a straight run of
losses (or wins) on a game of chance, the next chance of winning
(or losing) is going to be greater than what it would be if it
was their first attempt.  In problem (3) above, people tend to
say both are equally probably when in fact 60 boys out of 100 is
more probable.  And in problem (4) above most people think the
second ordering is more probable when in fact both sequences are
equally probable events.  People are mislead by how they think
probable or random events should "look like".
 
 
D.  REACTANCE
 
   Risk becomes particularly unacceptable in people's minds when
it is imposed by external circumstances over which we exert no
control, like the risks at work or from other people's mistakes.
We demand high standards at work so that we might have a barbecue
or go hang gliding on the weekend. Problem (5) actually occurred
with a community that was polled as to how to spend some money on
improving the safety of a particular motorway.  The citizens
chose crash barriers on the central divide, which on the
statistical list was about fifth down.  People want to reduce the
risk of what they can't control (that drunk driver coming towards
them) even if it means accepting a much greater risk from those
things that they think they do have some control over.
 
 
CONCLUSION:
 
     People as real-world decision-makers do not evaluate risk
and gains according to straightforward numerical probabilities of
expected value. Such oddities are explained, in part, by people
resorting to "heuristics" which by and large, work well enough
for many everyday judgements that need to be made in situations
of uncertainty.  But, they do not always work.  In the area of
risk/benefit estimates, we do very poorly.
 
 
 
References:
 
 John Scharffenberg     PROBLEMS WITH MEAT, 1989
 
 Keatin, M., et al.  Cardiovascular disease risk factors ...
     AMERICAN JOURNAL OF CLINICAL NUTRITION, 50(2):280, '89.
 
Thorogood, Margaret et al.  (1990)  Dietary intake and plasma
     lipid levels: lessons from a study of the diet of health
     conscious groups.  BRITISH MEDICAL JOURNAL, 300: 1297-1301.
 
 Phillips, R.,  Coronary heart disease mortality among seventh
     day Adventists with differing dietary habits.  ABSTRACT
     AMER. PUBLIC HEALTH ASSOC. MEETING Nov. 16-20, '75
 
 Ruys, J.,  Serum cholesterol . . . in Australian Adolescent
     vegetarians. BRITISH MEDICAL JOURNAL 6027:87, '76.
 
 Sacks, F.  Plasma lipids and lipoproteins in vegetarians and
     controls. NEW ENGLAND JOURNAL OF MEDICINE 292:1148, '75.
 
  Sacks, f., Blood ... in vegetarians.  AMERICAN JOURNAL OF
     EPIDEMIOLOGY 100:390, '74.
 
 Armstrong, B.  Blood...  AMERICAN JOURNAL OF EPIDEMIOLOGY
104:444, '78.
 
 Phillips, R.( 1979).  Coronary heart disease...differing dietary
     habits: a preliminary report.  AMERICAN JOURNAL OF CLINICAL
     NUTRITION 31:181, '78
 
 
Kahneman & Tversky (1972).  Subjective probability: A judgement
     of representativeness.  COGNITIVE PSYCHOLOGY, 3:430-54.
 
Kahneman & Tversky (1984).  Choices, values, and frames.
     AMERICAN PSYCHOLOGIST, 39: 341-50.
 
Slovic et al.  (1968).  Cognitive processes and societal risk
     taking.  In J. S. Carrol & J. W. Payne (Eds.), COGNITIVE AND
     SOCIAL BEHAVIOUR.  Hillsdale: Erlbaum.

Newsgroups: rec.food.veg