QUESTIONING EXPLANATIONS

Some pieces of reasoning, rather than trying to convince us that we should accept a
particular conclusion, aim instead to explain something which we already accept as being
true. This is a case of giving reasons why something is as it is, rather than giving reasons
for believing something. The difference is illustrated by the following report from The
Independent of 17 February 1994.
Latest figures for cancers in England and Wales show an increase of 4 per cent in
1988. Richard Doll, consultant to the Imperial Cancer Research Fund, said one
explanation was the rising number of elderly people.
Richard Doll’s comments are not trying to convince us of the fact that cancers increased in
1988. They are taking the truth of that for granted, and trying to explain why this increase
occurred.
This is a case of an explanation occurring as an independent piece of reasoning, but we may
also find explanations offered within an argument, as part of a longer passage of reasoning.
What we need to know about an explanation is whether it is the correct explanation. It
may not be easy to settle such a question, but there are strategies we can use to attempt to
make some assessment of an explanation. One is to examine any questionable assumptions
underlying the explanation. Another is to think of possible alternative explanations, and
try to find further evidence which may rule out some of these explanations. If we can
think of two or three equally plausible explanations of something, then we should be
cautious about accepting any of them as the correct explanation until we have further
information.
We can try these strategies on the above example, although it may seem presumptuous to
question the judgement of a leading authority in cancer research! What assumptions
underlie Richard Doll’s explanation? If the increase in cancers is attributable to ‘rising
numbers of elderly people’, this must be because people who, had they lived in earlier
times, would have died from other diseases (which are now more easily treatable or
preventable) are living to an age at which they are likely to get cancer. No doubt further
support for this assumption could be found by examining figures on the incidence of
cancer in different age groups.
What alternative explanations of the increase in cancer can we suggest? Well, there would
be an increase in cancer figures if the population in general were more susceptible to the
disease – perhaps because of pollutants in the environment. There would be an increase in
the figures if particular groups had a greater incidence of cancer, due to changes in habits
and practices. For example, it could be that new medications for circulatory diseases cause
more cancers, or that more cancers are caused by more women taking hormone replacement
therapy. Light could be shed on the plausibility of these alternative explanations
by examining figures on the incidence of cancer amongst different groups. We are not
suggesting that Richard Doll’s explanation is likely to be incorrect – in fact he is more
than likely to have taken all these factors into account before offering his explanation.
Possibly he meant that part of the increase in the incidence of cancer could be explained by
greater longevity. But the example serves to illustrate the way in which we can question
explanations, perhaps reserve judgement on them until we have more information, and
perhaps take steps to investigate which of various alternative explanations is the most
plausible.
The following passage describes a piece of research which aimed to find out the most
plausible explanation of a known fact. It is adapted from an article in The Independent on
Sunday, 25 June 1995.
Motorists in their teens and twenties have a low opinion of elderly drivers, whom
they regard as bumbling old fools who shouldn’t be allowed on the roads.
Some old drivers are indeed incompetent, and data from the US has shown that the
accident rate for drivers rises substantially after the age of 70. [A research team at
the University of California in Los Angeles has now carried out a detailed study of
the abilities of elderly drivers.]
The research team recruited volunteers in their early seventies who, according to
their doctors, had signs of early dementia due to Alzheimer’s disease, or to narrowing
of the arteries. Other drivers of the same age had diabetes as their only medical
condition, and a group of younger drivers was used for comparison.
All the drivers – the demented, the diabetics and the young controls – were taken
on a drive around a three-mile road network with intersections, speed bumps, traffic
signs, signals and parking lots. Each driver’s performance was graded by an
instructor in the car, which was fitted with an on-board computer which recorded
braking speed, steering, crossing the centre line, and so on. The drivers also worked
their way through a series of standard tests of mental ability, concentration and
short-term memory.
The results showed that the 70-year-olds with diabetes did just as well on the test
drives and mental tests as the younger drivers. The drivers with early dementia did
worse. They drove slowly, and the mistakes they made were serious – for example,
turning into a one-way street marked ‘no entry’.
The conclusion was that drivers in their 70s in normal health (with normal vision)
can perform at a level comparable with young, healthy adults – at least in a suburban,
non-stressing environment. Statistics showing that drivers in this age group
have high accident rates are, the report says, at least partly attributable to people
continuing to drive after they have become mildly demented.
(‘Second opinion’, Dr Tony Smith, The Independent on Sunday, 25 June 1995)
Before reading on, ask yourself the following questions:
• What was the known fact which the study sought to explain?
• What explanation would the author expect young motorists to give?
• What explanation does the report of the study give?
The passage tells us in the second paragraph that data from the US shows that the accident
rate for drivers rises substantially after the age of 70. This is the fact which is to be
explained, and it means, of course, that as a group the drivers aged over 70 have a higher
percentage of accidents than those aged under 70. It is clear from the first paragraph that
the author would expect young drivers to explain this fact by saying that all drivers aged
over 70 are incompetent, and therefore more likely to have accidents. The study did tests
to assess the competence of drivers, and found that those aged over 70 who had dementia
were less competent than young drivers, but those aged over 70 who did not have this
medical condition were no less competent than young drivers.
This suggests that the most plausible explanation of the higher accident rate amongst
drivers aged over 70 is that some drivers aged over 70 are incompetent due to dementia.
We should note that the article suggests that the driving test was conducted in a ‘suburban,
non-stressing environment’. If this is correct, then, in order to be certain that the
explanation offered by the study was the most plausible, we would want some evidence
about the competence of both young drivers and drivers aged over 70 in more stressful
traffic conditions.
The report does not make clear the age range of the ‘young control’ group. Dividing all
drivers into only two groups, over 70 and under 70, obscures any statistical differences in
the very large under-70 group. This is an example of how critical of statistics we must be,
even when we accept them. For example, drivers aged under 25 have a significantly higher
accident rate than those over 25. Elderly drivers might wish to argue that this showed a
high incidence of undiagnosed dementia among younger drivers!