Epistemology of natural sciences
Dr Tim Daw
School of International Development
University of East Anglia
t.daw@uea.ac.uk
Overview
• Epistemology – the nature of knowledge in
natural sciences
• The ‘scientific method’
– Popper – Falsification, Deduction
– Fisher - Statistical Hypothesis testing
– Quantification and statistics applied to Fisher and
Popper’s ideas
• A typical ‘scientific study’
– Tillman et al
• Problems with Null Hypothesis statistical testing
• Observational and modelling studies
• Complexity science, Systems ecology, Resilience
How do you know what you know?
How do know whether it is right?
What qualifies as Knowledge?
Monkeys can evaluate the
reliability of their knowledge!
How do scientists do it?
‘The scientific method’
• Basically POSITIVIST
– One reality is out there – there is a ‘truth’
– Objective research is possible
• Results depend on and reflect the nature of reality, not
the nature of the researcher
• Use of quantification and statistics to
objectively describe reality
• Generally REDUCTIONIST
– Examine the effects of one factor at a time...
Should the science of nature have a
different epistemology to the
science of human societies or
economies?
Induction
45
40
35
30
25
Y
Y is determined by X
20
15
10
5
0
0
5
10
15
20
25
X
What theory can explain
the nature of the data?
Deduction
45
40
35
30
25
Y
Y is determined by X
20
15
10
5
0
0
5
10
15
20
25
X
Does this data support
the theory?
Induction or Deduction?
•
•
•
•
•
Advantages of induction...
Disadvantages
What are you using in your research?
When would induction be useful?
When would deduction be useful?
DEDUCTION
Theory
Explanation
INDUCTION
Testing
Data
Popper – Science is...
• ‘Scientific’ and ‘unscientific statements’
• Theory can’t be proved, only disproved
‘The sun will always rise’
• Scientific statements must be falsifiable
• Science should be the process
of trying to disprove theories
• Natural selection of theories that
are not disproven
Karl Popper 1902 -1994
Applying numbers to deduction...
• Ronald Fisher
• Provided mathematical framework to
implement Popper’s falsification
– Null hypothesis, H0
– Statistical testing
– ‘Significance’
Ronald Fisher 1890-1962
Deduction with null
hypothesis testing
Y is unrelated to X
X = treatment
Y = response
Y is determined by X
What is the probability of data
if Ho is true?
e.g. P = 5% (unlikely)
45
40
35
30
25
Y
H0 is unlikely to be true...
20
15
10
5
0
0
5
10
15
X
20
25
Hypothesis is supported
How unlikely should the data be
in order to reject the null
hypothesis?
Why?
Tillman et al (1997)
• Background: Species extinction rates are ~1000 higher
than background rates
• Theory: Biodiversity is important for ecosystem
function
• Hypothesis: Changes in diversity will affect ecological
processes
• Treatment variables – Spp diversity and Func diversity
• Response variables – e.g. Biomass, Nutrients cycling etc
• Experiment: Manually manipulate diversity (treatment
variable) and measure processes (response variables)
• H0 – There is no relationship between diversity and
processes
Hypothesis: Biomass is a function of diversity
Biomass = an effect of Diversity + base level
Biomass ~ Diversity + Intercept
Null Hypothesis (H0):
– The effect of diversity is zero
Response variable
•
•
•
•
Treatment variable
Response ~ Spp Div + Func diversity + ‘intercept’
‘Non significant’ – H0 not rejected
Probability (of the data) if H0 is true is low
p < 1%, result is ‘significant’
H0 is rejected -> Theory is supported
But actually experiments are difficult
in ecology?
Graham et al 2008
What are the epistemological
implications of
- observational studies?
- Modelling studies?
Null hypothesis statistical tests
dominate the ecological literature
NHST
Inf theoretic
Other
NHST on
observations
Even though ecologists often have to rely on observational
data
Issues with H0 statistical tests
• Mis-interpretation
– ‘proving’ the null hypothesis
– Focus on the ‘p-values’
– Incomplete reporting and publication bias
• Philosophical issues
– Binary approach – Significant or not
Is that really the important question?
Stephens et al (2006)
Use of modelling
• Some of the most important Qs are not even
observable
• What will be the effect of ocean acidification on
marine fisheries?
Sumaila et al 2011
Alternative inferences
• ‘Information theoretic’ approaches (Burnham
& Anderson 2002)
• Compare alternative models (theories)...
Graham et al 2003
‘New Ecology’: changing epistemologies
• Complexity (see Berkes et al 2003)
– Multiple interacting factors
– Uncertainty
– non-linear relationships
• Human environment linkages
– Social-Ecological Systems (Berkes et al 2003)
–
Political
What
areEcology
the epistemological
– More holistic approaches
implications for ecologists studying
– Epistemological pluralism (Miller et al 2008)
linked
social-ecological
systems?
– Broader range of knowledges used (e.g. Local
knowledge)
Reductionism or Holism
Salvador Dalí - Nature Morte Vivante (Still Life - Fast Moving) (1956) Oil on canvas
Carpenter et al 2009
Range of epistemological approaches
in natural sciences
Theoretical
Experimental
Abstract
General
Empirical
Observational
Context
specific
Holistic
Reductive
Holistic
Reductive
Where does Tillman et al fit? For the most Natural scientist in your
group – where does their study fit?
References
• Berkes F, Colding J, Folke C (2003) Navigating social-ecological
systems: building resilience for complexity and change. Cambridge
Univ Pr
• Carpenter SR, Folke C, Scheffer M, Westley F (2009) Resilience:
accounting for the noncomputable. Ecology and Society 14:13
• Kornell N, Son LK, Terrace HS (2007) Transfer of Metacognitive Skills
and Hint Seeking in Monkeys. Psychological Science 18:64 -71
• Miller TR, Baird TD, Littlefield CM, Kofinas G, Chapin III FS, Redman
CL (2008) Epistemological pluralism: reorganizing interdisciplinary
research. Ecology and Society 13:46
• Stephens PA, Buskirk SW, Rio CM del (2007) Inference in ecology
and evolution. Trends in Ecology & Evolution 22:192-197
• Sumaila UR, Cheung WWL, Lam VWY, Pauly D, Herrick S (2011)
Climate change impacts on the biophysics and economics of world
fisheries. Nature Clim Change advance online publication
• Tilman D, Knops J, Wedin D, Reich P, Ritchie M, Siemann E (1997)
The Influence of Functional Diversity and Composition on
Ecosystem Processes. Science 277:1300 -1302