Philosophy of scientific inference

1
Philosophy of scientific inference
2
inductivism

• The method of induction starts with observation
  on nature .To the extent that the observation
  fall in to a pattern ,the observation are said to
  induce in the mind of observer a suggestion of a
  more general statement about nature

3
inductivism

• Jeners, observation of lack of smallpox among
  milkmaids.
• Boiling point of water

4
inductivism

• Causal inference based on mere coincidence of
  events constitutes a logical fallacy known as
  post hoc ergo propter hoc (after this therefore
  on account of this)

The crowing of a rooster is necessary for the
sun to rise because sunrise is always preceded by
the crowing
5
RefutationismPoppers philosophy

• A valid observation that is inconsistent with an
  hypothesis implies that the hypothesis as stated
  is false ,and so refutes the hypothesis .
• The single contrary observation caries more
  weight than thousands of repetition of the
  initial experiment .

6
Refutationism or falsification

• At any time ,hypotheses may be refuted by further
  observations and replaced by other hypotheses
  that better explain the observations

7
Thrombolytic Therapy
0.5
1.0
2.0
Cumulative
RCTs
Pts
1 23
2 65
3 149
4 316
7 1793
10 2544
Plt.01
11 2651
15 3311
17 3929
22 5452
23 5767
Plt.001
Odds Ratio (Log Scale)
Favours Treatment
Favours Control
8
Thrombolytic Therapy
Textbook/Review Recommendations
0.5
1.0
2.0
Cumulative
RCTs
Pts
1 23
Not Mentioned
Experimental
Rare/Never
Routine
Specific
2 65
3 149
21
5
4 316
7 1793
10
1
1
2
10 2544
Plt.01
11 2651
15 3311
8
2
17 3929
22 5452
7
23 5767
8
1
12
27 6125
Plt.001
8
M
30 6346
4
1
33 6571
M
7
3
1
43 21 059
M
54 22 051
Plt.00001
2
2
5
1
M
65 47 185
67 47 531
1
8
15
M
70 48 154
M
1
6
Odds Ratio (Log Scale)
Favours Treatment
Favours Control
9
Knowing is not enough we must apply.
Willing is not enough we must do.- Goethe
10
Consensus

• Some twentieth century philosopher of science ,
  most notably Thomas Kuhn have emphasized the role
  of the scientific community in determining the
  validity of scientific theories.
• Kuhn and others have argued that the consensus of
  the scientific community determines what is
  considered accepted and what is considered
  refuted .

11
(No Transcript)
12
The first published study on a scientific
question may find the most exaggerated effect
size and that as further evidence is gathered,
effect sizes tend to diminish.
Ioannidis, J. (2006).  Evaluation and
translation of research findings from bench to
where? PLOS Clinical Trials 1(7) e36.
doi10.1371/journal.pctr.0010036.
13
Thousands of observations are required before
estimates of gene disease associations became
stable.
14
The Hierarchy of Evidence

• Systematic reviews meta-analyses
• Randomised controlled trials
• Cohort studies
• Case-control studies
• Cross sectional surveys
• Case reports
• Expert opinion
• Anecdotal

15
Message (WHAT?)

• Actionable messages are preferable to single
  research reports or the results of single
  studies.

Actionable message Synthesis of research
knowledge Individual studies, articles and
reports Basic, theoretical and methodological
innovations