The Scientific Method Chapter 1. Overview What is Science? The Scientific Method From Hypothesis to Theory.

The Scientific Method

Chapter 1

Overview

What is Science?

The Scientific Method

From Hypothesis to Theory

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

Determining Variables

Factor, trait, or condition that can exist in different amounts or types

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

Control variable

Is kept constant

(so that will not affect outcome of experiment)

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

Limits of ScienceOnly testable hypotheses are valid

Some things are “unexplainable” or “untestable”

Supernatural, morality, etc.