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Casualty of phisiology
Causes are often distinguished into two types: necessary and sufficient.
If x is a necessary cause of y, then y will only occur if preceded
by x. In this case the presence of x does not ensure that y will
occur, but the presence of y ensures that x must have occurred.
On the other hand, sufficient causes guarantee the effect. So a
sufficient cause of y,presence x guarantees y. However, other events
may also cause y, and thus y's presence does not ensure the presence
Mackie argues that usual talk of "cause" in fact refers
to conditions insufficient and non-redundant parts of
unneccessary but sufficient causes. For example, consider
the short circuit as a cause of the house burning down.
Consider the collection of events, the short circuit,
the presence of oxygen, the flammability of the house,
and the absence othese are unnecessary but sufficient
to the house's destruction since many other collection
of events certainly could have destroyed the house Within
this collection, the short circuit is an insufficient
but non-redundant part (since the short circuit by itself
would not cause the fire, but the fire will not happen
without it. So the short circuit is an cause of the
house burning down.
Causality contrasted with logical implication
Logical conditional statements are not statements of causality.
Since logical conditional statements and causal statements are both
presented using "If...then..." in English they are commonly
confused;distinct, however. The standard conditional statement expresses
a fact about the actual world, while causal statements imply something
more. For example all of the following statements are true terpreting
"If... then..." as the logical conditionalIf George Bush
was president of the United States in , then Germany is in Europe
If George Washington was president of the United States in thenGermany
is in Europe The second and third are both true because the antecedent
is false. Of urse, none of these statements express a causal connection
between the antecedent and consequent.Another sort of logical implication,
counterfactual implication has a stronger connection with causality.
However, not even all counterfactual statements count as examples
of causality. Consider the following two statements:
In the first case it would not be correct to say that A's being
a triangle caused it to have three sides, since the relationship
between triangularity and three-sidedness is one of definition.
Nonetheless, even interpreted counterfactually, the first statement
is true. Most sophisticated accounts of causation find some way
to deal with this distinction.
Counterfactual theories of causation
The philosopher David Lewis notably suggested that all
statements about causality can be understood as counterfactual statements
(Lewis 1973, . So, for instance, the statement that John's smoking
caused his premature death is equivalent to saying that had John
not smoked he would not have prematurely died. In addition, it need
also be true that John did smoke and did prematurely die, although
this requirement is not unique to Lewis' theoryOne problem Lewis'
theory confronts is causal preemption. Suppose that John did smoke
and did in fact die as a result of that smoking. However, there
was a murderer who was bent on killing Joand would have killed him
a second later had he not first died from smoking. Here we still
want to say that smoking caused John's death. This presents a problem
for Lewis' theory since, had John not smoked, he still would have
died prematurely. Lewis himself discusses this example, and it has
received subsantial discussion. Ganeri, Noordhof, and Ramachandran
Paul
Probabilistic causation
Interpreting causation as a deterministic relation means that if
A causes B, then A must always be followed by B. In this sense,
war does not cause deaths, nor does smoking cause cancer. As a result,
many turn to a notion of probabilistic causation. Informally, A
probabilistically causes B iff A's occurrence increases the probability
of B. This is sometimes interpreted to reflect imperfect owledge
of a deterministic system but other times interpreted to mean that
the causal system under study has an inherently chancy nature.
The establishing of cause and effect, even with this relaxed reading,
is notoriously difficult, expressed by the widely accepted statement
"correlation does not imply causation". For instance,
the observation that smokers have a dramatically increased lung
cancer rate does not establish that smoking must be a cause of that
increased cancer rate: maybe there exists a certain geneticefect
which both causes cancer and a yearning for nicotine.In statistics,
it is generally accepted that observational studies like counting
cancer cases among smokers and among non-smokers and then comparing
the two can give hints, but can never establish cause and effect.
The gold standard for causation here is the randomized experiment:
take a large number of people, randomly divide them into two groups,
force one group to smoke and prohibit the other group from smoking
ideally in a double-blind setup), then determine whether one group
develops a significantly higher lung cancer rate. Random assignment
plays a crucial role in the inference to causation because, in the
long run, it renders the two groups equi in terms of the outcomeso
that any changes will reflect only the manipulation smoking. Obviously,
for ethical reasons this experiment cannot be performed, but the
method is widely applicable for less damaging experiments. One limitation
of experiments, however, is that whereas they do a good job of testing
for the presence of some causal effect they do less well at estimating
the size of that effect in a population of interest. This is a common
criticism of studies of safety of food additives that use doses
much higher than what people consuming the product would actually
ingest
That said, under certain assumptions, parts of the causal structure
among several variables can be learned from full covariance or case
data by the techniques of path analysis and more generally, Bayesian
networks. Generally these inference algorithms search through the
many possible causal structures among the variables, and remove
ones which are stron incompatible with the observed correlations.
In general this leaves a set of possible causal relations, which
should then be tested by designing experiments. If experimental
data is already available, the algorithms can take advantage of
that as well. In contrast Bayesian Networks, path analysis and its
generalization, structural equation modeling, serve better to estimate
a known causal effect or test a causal model than to generate causal
hypotheses.
For nonexperimental data, causal direction can be hinted if information
about time is available. This is because causes must precede their
effects temporally. This can be set up by simple linear regression
models, for instance, with an analysis of covariance in which baseline
and followup values are known for a theorized cause and effect.
addition of time as a variable, causality, is a big help in supporting
a pre-existing theory of causal direction. For instance, our degree
of confidence in the direction and nature of causality is much clearer
with a longitudinal epidemiologic study than with a cross-sectional
one.
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