Post on 22-Dec-2015
What is Science?
The goal of science is to understand natural phenomena
2 types of science:
• Discovery science
• Hypothesis-based science
Four-eyed butterfly fish
Discovery ScienceDescribes nature
Uses inductive reasoning
Observations used to infer conclusions (but no complete certainty as to validity)
e.g. This red jellybean tastes like cherry. Thus, all red jellybeans taste like cherry.
= ?
Hypothesis-Based Science
Uses deductive reasoning
Previously-known premises used to form conclusions (as long as
premises are correct, conclusion will be too)
e.g. Dogs are mammals.All mammals have hair or fur.Thus, all dogs have hair or fur.
Critical Thinking
Using data and facts to make inferences, draw
conclusions, solve problems, etc.
Should be unbiased thought but rarely is
The Scientific Method
Investigation of biological systems
• Observation
• Hypothesis
• Predictions
• Test
• Analysis of results
• Conclusion
Formulating a Hypothesis
Proposes the answer to a question about an observation
e.g. Exposure to fertilizer increases reproduction of bean plants
A Good Hypothesis …
Must be testable and falsifiableA hypothesis can be falsified but can never be proven
true: evidence can only support
Scientific knowledge is ever expanding as new methodologies are applied to old questions,
etc.
Examples of Good Hypotheses:
• Cactus spines reduce herbivory
• UVB radiation causes limb deformities in amphibians
Examples of Untestable Hypotheses:
• Women are more moral than men
• Dogs are smarter than cats
Testing a Hypothesis
Scientific experiment(either falsifies or supports a hypothesis)
• Make predictions
• Determine variables
• Design an experimental procedure
• Carry out procedure
Making PredictionsBased on an experiment designed to test a
hypothesis
If/then statements:“If the hypothesis is true, then the results of the
experiment will be …”
e.g. If exposure to fertilizer increases reproduction of bean plants, then the number of pods per plant should increase in plants exposed to
fertilizer compared with control plants.
If results match prediction, hypothesis is supported
If not, the hypothesis is falsified
Knowledge of process has been increased either way, regardless of findings
Independent variable
The variable of interest
Is deliberately manipulated (changed)
Only one is usually chosen(need to know which factor is affecting the
dependent variable)
Dependent variable
Is measured or observed during an experiment
Value is caused by and depends on the value of the independent variable
e.g. Exposure to fertilizer increases reproduction of bean plants
Independent: fertilizer
Dependent: number of bean pods
Control: Other things that would affect bean reproduction e.g. amount of water, temperature, amount of light, etc.
ExamplesThe relationship between drug dosage &
frequency / intensity of symptomsIndependent: amount of drug administered (dosage)
Dependent: Frequency / intensity of symptoms
The relationship between plant growth rate & duration of light exposure
Independent: Amount of time of exposure to light
Dependent: Plant growth rate
Designing a Procedure
Methodology for an experiment
Quantitative (counts/measurements) methods usually better than qualitative (descriptive)
(allows re-testing of hypothesis by same or others)
Control Treatment
Independent variable either held at a standard value or omitted
Results compared between control and experimental treatments
Allows scientist to decide if predicted effect is due to independent variable or random
chance
Examples
Researchers want to test the effects of a drug for treating a medical condition. To ensure
that the drug actually works, they would use a control group of people …
… who take a placebo drug
Researchers want to see the effects of drinking caffeinated water. The control group…
… would drink plain water
Level of Treatment
Values set for independent variable
(based on prior knowledge/previous research)
Can be:• One specific value (e.g. specific temperature)• Range of values (e.g. range of temperatures)
Some experiments have no level of treatment• e.g. gender
Replication
Procedure is repeated several times to see if results are consistent
Gives an idea of how much variation is present
Results from different trials are averaged
Sample SizeLarger sample size = greater confidence
Mean & standard deviations of sample differ from that of population from which taken
Larger sample size = lower sampling error
Sampling Error
Exposure to fertilizer increases reproduction of bean plants
Level of treatment:– Specific amount of fertilizer OR
– Range of amounts/concentration of fertilizer
Control:– Beans grown without applying fertilizer
Replication and sample size:– Depends … the more the better
Presenting & Analyzing Results
Analysis:Simple to advanced statistics
Presentation:Tables and/or figures
• Show relationships between independent and dependent
variables• Bar graphs vs. line graphs
More on this in next week’s lab
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Drawing Conclusions
Results are interpreted:Was hypothesis supported or falsified?
If supported:Additional experiments suggested to further support
hypothesis(using same or different methods)
If falsified:Alternative hypotheses for testing suggested
Exposure to fertilizer increases reproduction of bean plants
If more pods found on plants treated with fertilizer:
Hypothesis is supported
Could try different amounts/concentrations of fertilizer, different fertilizers, etc.
Could also see if combination of variables affects reproduction e.g. fertilizer & water,
fertilizer & light
Exposure to fertilizer increases reproduction of bean plants
If no significant difference in number of pods on beans in either treatment (control or
experimental):
Hypothesis is falsified
Could try testing other factors e.g. temperature, amount of water, amount of
light, etc.
From Hypothesis to Theory
How does something become a scientific theory?
When multiple rigorous tests have not disproved a certain hypothesis
(i.e. an idea with “great explanatory power”)
A theory can be used to interpret other data and observations