Scientific Method and Experimentation

Two ways of thinking

• Induction– Form of thinking in

which one starts with a number of separate observations and then arrives at general principles

• Deduction– Form of thinking in

which one reasons from general principles to specific conclusions

*BOTH METHODS ARE INDISPENSIBLE*

INDUCTION

INDUCTION

• Make a series of individual observations

• IDEALLY, Have no goal or hunch as to outcome

INDUCTION

• Example– Suppose a particular marine biologist

examined a sailfish, a shark, and a tuna, and found that they all had gills. Since sailfish, sharks, and tuna are all fishes, he might draw the general conclusion:

• ALL FISH HAVE GILLS

INDUCTION

• PITFALLS– The number and quality of the observations is critical

in developing a general statement

– If the biologist had only examined sailfish, which happen to have a bill, he might use information to develop a false statement, “ALL FISH HAVE BILLS.”

– Even after examining all three types of fish he may have concluded, “ALL MARINE FISH HAVE GILLS” instead of just “ALL FISH HAVE GILLS”

DEDUCTION

DEDUCTION

• Start with a general statement about nature

• Predict what specific consequences would be if the general statement is true

DEDUCTION• In the process of

deduction, applying a general principle allows one to make specific predictions

• The scientist may arrive at the general statement by intuition or hunch, but most often the statement is the result of INDUCTION

THEREFORE DEDUCTION AND INDUCTION ARE LINKED!!!!!!

DEDUCTION

• LIMITATIONS– Suppose the general statement is, “ALL

MARINE ANIMALS HAVE GILLS”

May lead to the assumption that DOLPHINS have gills since they live in the water

INDUCTION + DEDUCTION

• Both induction and deduction lead scientists to make a statement that might be true

• Scientists need to test these statements to see whether they are, in fact, true

HYPOTHESIS

• A statement that might be true

• Must be tested, usually over and over again

• Constructing a hypothesis– Hypotheses must be

stated in a way that enables them to be tested

– It must be possible to prove the hypothesis false, if it is false

HYPOTHESIS

• Example– Hypothesis “WHALES HAVE GILLS”

• Examine a whale to see whether it has gills

• Discover whales have lungs not gills

• Disproves hypothesis, “WHALES HAVE GILLS”

• Also disproves more general hypothesis, “ALL MARINE ANIMALS HAVE GILLS”

HYPOTHESIS

• Pitfalls– Propose a hypothesis that cannot fairly be tested

– Example• “SOMEWHERE IN THE OCEAN THERE ARE

MERMAIDS”

• Scientists may never find a mermaid, but believer could say “THE MERMAIDS ARE THERE YOU JUST DIDN’T FIND THEM”

• No matter how hard you look you can never prove there are no mermaids

• “THERE ARE NO MERMAIDS IN THE OCEAN” is not a valid hypothesis

HYPOTHESIS

• Overview

– A scientific hypothesis is a statement about the world that might be true and is TESTABLE

– A testable hypothesis is one that at least potentially can be FALSE

The Nature of Scientific Proof

• It must be at least possible to disprove a hypothesis before the hypothesis can be considered scientific

• Ways to Prove a Hypothesis True– In general, no

scientific hypothesis can be proven ABSOLUTELY TRUE

– There are no absolute truths in science

The Nature of Scientific Proof• Scientific hypotheses are tested repeatedly to see

if they agree with actual observations of the world• A hypothesis that withstands repeated testing is

provisionally accepted as true• EXAMPLE

– Scientists accept the hypothesis “ALL FISH HAVE GILLS” because every attempt to reject it has failed

NO hypothesis can be scientifically proven true!!!!!

Hypotheses are accepted for as long as the available evidence supports them!!!

Testing the Hypothesis

Testing the Hypothesis

Testing the Hypothesis

• Problem– Do oysters grow faster in warm or cold water?

• Approaches– Find two places, one warm, one cold and

measure how fast the oysters grow at each place

Testing the Hypothesis

• Pitfall– The temperature at

any given place will change all the time. Biologists would have difficulty finding two locations where one is always warmer than the other

• May be other differences!!!– Different types of food

– Different amounts of food

– Pollution

– Outbreak of disease

– AND MANY MORE!

Testing the Hypothesis

• In any natural setting there will be countless factors to consider other than the one to be tested for

• Factors that might affect observations are called variables

• Overcoming pitfalls– Run experiment in holding tanks where extraneous

variables such as amount and type of food can be controlled

– Controlled variable• Variable that scientists artificially keeps from changing to

prevent it from affecting the experiment

The Scientific Theory

• A theory is a hypothesis that has passed so many tests that it is generally regarded as true

• Theories, like hypotheses, cannot be absolutely proven

• Theories are only accepted so long as they are supported by evidence

• A scientific theory is a hypothesis that has been so extensively tested that it is generally regarded as true. Like any hypothesis, it is subject to rejection if enough evidence accumulates against it

Limitations of the Scientific Method

• No one can be absolutely objective at all times, personal biases may affect thinking

• Science can not make judgments about values, ethics, or morality

Methods of Conducting Experiments

• Experiment– A study in which the investigator manipulates

at least one other variable

• Independent Variable– The variable the investigator manipulates

• Dependent Variable– The variable that is measured, that changes in

response to the independent variable

Methods of Conducting Experiments

• Experimental Group– Receives the treatment

that the experiment is designed to test

• Control Group– Is treated in the same

way as the experimental except for the experimental treatment

Methods of Conducting Experiments

• Single Blind Studies– Subjects are unaware

of which subjects received the treatment

– Placebo• Inactive Pill

– Blind Observer• An observer who does

not know which subjects are in which group and what is expected of each

• Double Blind Study– Both the observer and

subjects are unaware

General Principles of Conducting Research

• Defining Variables– Examples

• Decide what terms like “motivation” or “love” mean

– Psychologists use operational definitions• A definition that specifies the operations or procedures used

to measure some variable or produce some phenomenon

• Example– Love the amount of time a person will go without a personal

need to take care of another’s needs

General Principles for Conducting Research

• Random Sample– Every individual in the

population has an equal chance of being selected

• Relative Sample– Closely resembles the

entire population in its percentage of males and females, ethnic groups, religions, etc.

Evaluation of Evidence

• Replicable Results– Anyone who repeats the same procedure will

get the same resultsTrial 1 Trial 2

Theories

• Comprehensive explanations of natural phenomena that lead to accurate predictions

• Criteria for evaluating scientific theories– Good theories

• Reveals patterns in the observations we make

• Predicts new observations

• Is falsifiable

• Is parsimonious