Epistemology of natural sciences

Dr Tim DawSchool of International Development University

of East Angliat.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

TheoryY is determined by X

What theory can explain the nature of the data?

Empirical research

Data

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25

Y

X

Deduction

TheoryY is determined by X

Does this data support the theory?

Empirical research

Data

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25

Y

X

Induction or Deduction?• Advantages of induction...• Disadvantages• What are you using in your research?• When would induction be useful?• When would deduction be useful?

Explanation Testing

Theory

Data

DEDUCTION

INDUCTION

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

Theory/HypothesisY is determined by X

What is the probability of data if Ho is true?

e.g. P = 5% (unlikely)

Experimental research

Null Hypothesis H0

Y is unrelated to X

H0 is unlikely to be true...

Hypothesis is supported

Data

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25

Y

X

X = treatmentY = response

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

Treatment variable

Resp

onse

var

iabl

e

Response ~ Spp Div + Func diversity + ‘intercept’

‘Non significant’ – H0 not rejectedProbability (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

NHSTInf theoreticOtherNHST onobservations

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 Ecology– More holistic approaches– Epistemological pluralism (Miller et al 2008)– Broader range of knowledges used (e.g. Local

knowledge)

What are the epistemological implications for ecologists studying linked social-ecological systems?

Reductionism or Holism

Carpenter et al 2009

Salvador Dalí - Nature Morte Vivante (Still Life - Fast Moving) (1956) Oil on canvas

Range of epistemological approaches in natural sciences

Theoretical Empirical

AbstractGeneral

Context specific

Holistic Reductive

Experimental Observational

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