Philosophy of science: the scientific method

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Philosophy of science the scientific method
Science
A method for achieving this goal
Development of theory
Formulation of hypotheses - predictions
Tests of predictions
Design Analysis
How we test predictions of hypotheses
Statistics
Tool for quantitative tests
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Definitions
Theory a set of ideas formulated to explain
something
Hypothesis general supposition or
conjecture put forth in the form of a
prediction according to a theory,
observation, belief, or problem specific
formulation of a general hypothesis for
application to a specific test (observational
OR experimental)
Null hypothesis expected outcome if supposed
mechanism is not manifested (i.e. no effect)
Predictions expected outcomes if both
assumptions and conjecture are correct
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Definitions (examples)
Theory species distributions determined by
dispersal of offspring
Hypothesis general larval settlement of
mussels determines adult distribution (i.e. is
restricted to the area inhabited by adults)
specific if we sample larval settlement of
mussels in and out of adult distribution, then
settlement will only occur within area inhabited
by adults
Null hypothesis if we sample larval settlement
of mussels in and out of adult distribution,
there will be no difference in settlement
Predictions theory predicts that larval
settlement will only occur where adults are
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Definitions
Induction (or inductive reasoning) reasoning
that general laws exist because particular
cases that seem to be examples of it
exist
Deduction (or deductive reasoning) reasoning
that something must be true because it is
a particular case of a general (universal)
law known to be true
induction
specific
general
deduction
all swans are white
5 swans seen, all are white
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Examples
Induction (or inductive reasoning) Every swan I
have seen is white, therefore all swans are
white (if) (particular/observation), (then)
(universal/ inference)
Deduction (or deductive reasoning) All swans
are white, therefore next swan I see will be
white (if) (universal/ theory), (then)
(particular/observation)
DIGS deductive is general to specific
Comparison
1. Which is more testable? What if next swan is
not white?
2. Which is normally used in everyday experience?
3. Which is more repeatable by different people?
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Hypothetico-deductive reasoning
Deduction (or deductive reasoning) formalized
and popularized as basis of scientific method
by Karl Popper (in readings)
Two phases conception and assessment
Conception how one comes up with a new idea or
insight (rules of formulation are not obvious).
-- theory, observation, belief, problem
-- creative, difficult to teach, but often
inductive!
Assessment deductive phase, should be
repeatable
Together, hypothetico-deductive reasoning
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Hypothetico-deductive reasoning
Perceived Problem
I. Conception
Largely inductive reasoning
Belief
Previous Observations
Note General hypothesis stated as
alternative HA to null HO
INSIGHT
Existing Theory
General hypothesis
II. Assessment
Specific hypotheses
Deductive reasoning
(and predictions)
Comparison with new observations or experimental
results

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Hypothetico-deductive reasoning Platts (1964)
Strong Inference

• Is there provision for accepting general
  hypothesis?
• Why not?

Because it is easy to find confirmatory
observations for almost any hypothesis, there is
always the possibility of a negative result yet
to be tested, and only one negative result
refutes it absolutely
2) Propositions not subject to rejection (not
falsifiable) are not scientific.
3) Progress made by repeated testing (rejection
or confirmation) of alternative hypotheses until
all reasonable ones have been tested (last man
standing).
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Example Platts (1964) Strong Inference

1. Observation discrete distributions of
   vegetation along elevation gradient (zonation)
   adjacent to Younger Lagoon

(S)
(R)
(A)
Anise (A)
100
percent cover
Rush (R)
50
Salicornia (S)
0
0
2
4
6
8
elevation (m) above mean water level
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Example Platts (1964) Strong Inference

1. Observation discrete distributions of
   vegetation along elevation gradient (zonation)
   adjacent to Younger Lagoon

Is there any existing theory to explain this
pattern?
Limits of species distributions often set by
their relative tolerance to physical factors
-- water immersion -- salinity --
desiccation -- soil characteristics
Insight distribution limits set by tolerance
to water immersion

• General hypothesis (HA) lower limit of rush
  set by tolerance to immersion
• alternatively, null hypothesis (Ho) of no
  effect of immersion on lower limit of rush
  distribution

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Example Platts (1964) Strong Inference

1. General hypothesis lower limit of rush set
   by tolerance to immersion

(alternatively, null hypothesis of no effect of
immersion on lower limit of rush
distribution)

1. Specific hypotheses

Observational HA average water level
coincides with lower limit of rush Ho no
relationship between water level and lower
limit. Experimental HA rush plants
transplanted to clearing below lower limit
will die. Ho no difference in survival
between transplants and controls
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Example Platts (1964) Strong Inference
4a) Test of prediction repeatedly observe
water levels and find that lower limit of
rush coincides with mean water level (?
confirm hypothesis that lower limit set by
immersion).
Consider other tests (e.g., other species)
of general hypothesis
4b) Test of prediction repeatedly observe
water levels and find that lower limit of
rush does NOT coincide with mean water
level (? reject hypothesis that lower limit
set by immersion).
Consider other alternative hypotheses until
you cant reject one.
5a,b) Parallel results and conclusions from
experimental tests of predictions Why??
correlation vs. causation
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Example Platts (1964) Strong Inference
1) Observation (or theory) ? Question
2) General hypothesis (question rephrased as
testable statement)
3) Specific hypothesis (that state testable
predictions that are directly related to how
you would test the general hypothesis)
4) Test(s) of prediction(s)
confirm hypothesis ? consider other tests of
general hypothesis to possibly reject or
further substantiate
reject hypothesis ? consider other alternative
hypotheses until you cant reject one.
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Problems
1) This process leads to paradigms, a way of
thinking that has many followers, with great
inertia. Contrary evidence considered an
exception rather than evidence for falsification.
2) Some (e.g., Roughgarden) argue that this is
not how we do science, but rather by building a
convincing case of many different lines of
evidence (i.e. inductive conception and
assessment)
3) Others (e.g., Quinn Dunham) argue that
ecology, in particular, is too complex (many
variables that interact with one another) to
devise unequivocal tests. Examples importance
of process (e.g., competition) is context
dependent (e.g., environmental harshness or
recruitment limitation)
4) In ecology, were often interested in
relative effects and strengths of effects (rather
than mere presence absence of effects).
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Rigorous ScienceBased on absolute or probability
values?The linkage between Popperian science
and statistical analysis
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Absolute vs. measured differences
Philosophical underpinnings of Popperian Method
is based on absolute differences

A)
E.g., All swans are white, therefore the next
swan I see will be white.
If the next

swan is not white, then the hypothesis is refuted
absolutely.

Instead, most results are based on comparisons of
measured variables

B)
not really true vs. false but degree to which an
effect exists (recall Quinn and Dunham)



Example
-
General or working hypothesis larval
settlement determines adult distribution


Specific hypothesis number of mussel larvae
settling is higher in areas inside the adult
distribution than in areas outside it

Number inside
What counts as a difference? Are these different?