- Inductive method: the scientist
gathers empirical* data and from it arrives at a generalization
- Deductive method: a scientist
develops a general idea about a phenomena, performs experiments and from
them makes specific predictions that can be tested again
- The inductive approach is the
formation of general principles from specific observations
- The deductive approach is the
prediction of specific events from general principles
*empirical: based on observation, not
theory or logic.
- Ecologists employ direct
observation and comparison in "natural experiments".
- Example: Dead Trees/Woodpeckers
- The observed patterns only suggest
a correlation (co-related)
- They do not address the question
of cause and effect
- This rigorous establishment of causation is
what separates science from unwarranted assumptions about reasons for
- Assume the investigator has developed
a hypothesis that elevated levels of CO2 result in increased
- Plant growth response to elevated CO2 is
the dependent variable and the concentration of CO2 is
the independent variable.
- The investigator wants to know the
effect of varying the independent variable.
- The next step is to collect the data
necessary to test the hypothesis and reach a conclusion.
- The experimental data would consist of
growth measures (e.g. biomass gain over a period of time) for plants grown
under ambient (the control samples) and elevated levels of CO2 (treatment
- We test the hypothesis statistically
by creating a
- null hypothesis (H0)
- alternative hypothesis (H1)
- In the present experiment the null
hypothesis would state that the elevated levels of CO2 have no
effect on growth, because generally in an experiment it is easier to
disprove a null hypothesis than to prove a hypothesis.