scientific method 2015 ss

PowerPoint Lecture prepared by

Dr. Judi Roux,

University of Minnesota Duluth

Chapter 1

Can Science Cure the Common

Cold?

Introduction to the Scientific Method

© 2016 Pearson Education, Inc.

Learning Outcomes

• Describe the characteristics of a scientific hypothesis.

• Compare and contrast the terms scientific hypothesis and scientific theory.

• Distinguish between inductive and deductive reasoning.

• Explain why the truth of a hypothesis cannot be proven conclusively via deductive reasoning.

• Describe the features of a controlled experiment, and explain how these experiments eliminate alternative hypotheses for the results.


Learning Outcomes

• List strategies for minimizing bias when designing experiments.

• Define correlation, and explain the benefits and limitations of using this technique to test hypotheses.

• Describe the information that statistical tests provide.

• Compare and contrast primary and secondary sources.

• Summarize the techniques you can use to evaluate scientific information from secondary sources.


Basic Steps to the Scientific Method

1. Make observations. Is there a trend?

If X happens, Y happens.

2. Make a hypothesis – a statement that you can test

3. Design an experiment to change one condition (X) and measure another condition that might change as a result (Y).

4. Collect data.

5. Analyze results – Do the data support the trend?

6. Repeat.

What advice do you receive from friends and family to treat your cold?

A. Take vitamin C.

B. Use zinc lozenges.

C. Drink echinacea tea.

D. Meditate.

E. Get more rest.

F. Wear a warm hat.

G. Eat chicken soup.


1.1 The Process of Science

Science is…

• a body of knowledge

• E.g., biology, the study of living organisms

• the discovery of something new and unknown



Science is NOT…

• recalling specific facts about the world.

• memorizing what is already known.



The scientific method

• Making observations

• Proposing ideas

• Testing the ideas

• Discarding or modifying ideas based on results



Observations lead to questions.

Hypotheses are proposed explanations for those observations.



Your mom’s observation: It’s cold outside.



Your mom’s observation: It’s cold outside.

Your mom’s hypothesis: Dressing warmly will help you avoid a cold, because becoming chilled makes you more susceptible to illness.


“Colds are generated by disturbances in psychic energy” is a testable statement.

A. True

B. False



The Nature of hypotheses

• Scientific hypotheses

• Testable: possible to evaluate

• Falsifiable: potentially false


Which statement is a scientific hypothesis?

A. Jazz is better music than rap.

B. Garden fairies make tomatoes grow better.

C. Hunting species to extinction is wrong.

D. Increasing the amount of protein in a cow’s diet increases milk yield.



Everyday use of “theory”

• Untested ideas based on little information

Scientific theory

• Powerful, broad explanation for related observations

• Based on well-supported hypotheses

• Supported by different, independent lines of research



Chronic stomach ulcers

• Common belief: Ulcers are caused by acids and spicy foods.

• Treatment: drugs to reduce acid; avoiding spicy food

• New observation: Helicobacter pylori bacteria were found in most samples of ulcer tissue.



Chronic stomach ulcers

• Accepted fact: H. pylori infections cause stomach ulcers.

1. No reasonable alternative hypotheses are supported.

2. The hypothesis has not been rejected by carefully designed experiments.

3. The relationship between H. pylori and stomach ulcers follows the germ theory of disease.

1. That is, the patients carry the same, recognized pathogen



Fact 1: Fruits and vegetables contain muchvitamin C.




Fact 2: People with diets rich in fruits andvegetables are generally healthier.





Fact 3: Vitamin C is an anti-inflammatory agentthat reduces throat and nose irritation.





Fact 3: Vitamin C is an anti-inflammatory agentthat reduces throat and nose irritation.

Hypothesis: Consuming vitamin C decreasesthe risk of catching a cold.

Inductive reasoning: combining specific observations to a general principle



Hypothesis: Consuming vitamin C decreases the risk of catching a cold.

• Sensible

• Needs to be tested

• May be proven false



The logic of hypothesis tests

• Hypothesis testing based on

• Deductive reasoning –General principle to predictobservations

• If/then statements formaking predictions



The logic of hypothesis tests

• Prediction is true

• Hypothesis is supportedbut NOT proven

• Prediction is false

• Hypothesis rejectedand disproven


Why is it impossible to say that the hypothesis that vitamin C prevents colds is true?

A. Lab experiments are not practical.

B. Alternative hypotheses might be possible.

C. Experiments with humans are unethical.

D. Vitamin C cannot be obtained naturally.


1.2 Hypothesis Testing

Hypothesis: The common cold is caused by a virus.

• Tested by experiments

• Supported by experimental results.


All hypotheses need to be tested with laboratory experiments.

A. True

B. False

Explanation: Some hypotheses may be tested by observations of fossils.



The experimental method

• Experiments

• Collect data or information

• Test specific hypotheses

• Example: Scientists will measure the effectsof vitamin C on cold prevention



The Experiment: To measure the effect of vitamin C on cold prevention

Variables: factors that may change

• Independent variables: those manipulated by the researcher

• Vitamin C intake

Can only change ONE condition! If the researcher changes more than one, then don’t know what might be causing the experimental result.

Must have a baseline or “zero” - that is, a

CONTROL = where the change hasn’t been made

• Something to compare your manipulation to . . .



The Experiment: To measure the effect of vitamin C on cold prevention

Variables: factors that may change

• Independent variables: those manipulated by the researcher

• Vitamin C intake

• Dependent variables: those not changed by the researcher; may change during the experiment

• Susceptibility to illness upon exposure to virus

Note that like independent variable, you must be able to measure any changes in the dependent variables – see it, smell it, etc., and track it !



Controlled experiments

• Test the effect of a single variable

• Able to measure the changes in independent variable (“control”)

• Able to measure any changes in dependent variables – In this example, whether the cold doesn’t occur or is less severe

• Limit possible alternate hypotheses - That is, nothing except the independent variable changes “Controlled Variables” = conditions that do not change.

• Differences in results should only be due to independent variable - In this example, the treatment for the cold



Control or control group

• Similar to experimental subjects

• Do NOT receive the experimental treatment



Steps for controlled experiments

1. Random assignment to control or experimental group

2. Identical participation for both groups except forthe testing treatment



Echinacea tea experiment

• Hypothesis: Drinking echinacea tea relieves cold symptoms.

• Experimental group drank echinacea tea5–6 times daily

• Control group drank “sham” tea (placebo)





• Independent variable:drinking tea

• Dependent variable:relief from cold symptoms





• Independent variable:drinking tea

• Dependent variable:relief from cold symptoms

• Results: Experimental group felt echinacea tea was 33% more effective.



Minimizing bias in experimental design



Minimizing bias in experimental design

• Bias: influence on results

• Blind studies: limit participant knowledge

• Double-blind studies: also limit researcher knowledge of participant groups



Using correlation to test hypotheses

• When controlled experiments on humans may be

• Impossible

• Dangerous

• Unethical




• Model systems: used to avoid unethical or impractical tests on humans

• Bacteria

• Nematodes

• Mammals(rodents, dogs,pigs, human cells)



Relationships between factors

Hypothesis: Stress makes people more susceptible to catching a cold.

• Is there a correlation between stress and the number of colds people have caught?




• Results: The number of colds increases as stress levels increase.


Stress may NOT increase the number of colds, even though a correlation exists between the two factors.

A. True

B. False




• Results: The number of colds increases as stress levels increase

• Caution! Correlation does not imply causation




• The correlation might be due to other reasons


1.3 Understanding Statistics

Overview: What statistical tests can tell us

• Statistics in science

• Evaluate and compare data

• Statistical tests

• Examine variabilitybetween groups

• Results fromsample may extendto entire population



Overview: What statistical tests can tell us

• Statistically significant

• Results show a true difference between groups

• Low probability that difference between groups is due to random chance

• Researchers may infer that treatment had an effect



The problem of sampling error



The problem of sampling error

• Sampling error: the effect of chance on experimental data

• Confidence interval:range of values witha 95% probability ofcontaining the truepopulation mean(average)



Factors that influence statistical significance



Factors that influence statistical significance

• Sample size

• The true difference between populations



What statistical tests cannot tell us

• If an experiment was designed and carried out properly

• If observer error occurred; can evaluate only the probability of sampling error

• May not be of any biological significance


1.4 Evaluating Scientific Information

Science in the news

• Primary source:original research

• Secondary source:story about the original research



Anecdotal evidence

• Based on one person’s experience, not on experimental data.

• Example: a testimonial from a celebrity


What is the best way to prevent the common cold?

A. Take vitamin C.

B. Wash your hands.

C. Take zinc lozenges.

D. Get a cold vaccine.

Explanation: Washing hands isthe only method that has beenshown to prevent the commoncold.


1.5 Is There a Cure for the Common Cold?

• No cure or vaccine

• Best prevention: Keep your hands clean!

• No effect on cold susceptibility:

• Vitamin C

• Diet quality

• Exposure to cold temperatures

• Exercise

• But may reduce cold symptoms:

• Vitamin C

• Echinacea tea

• Zinc lozenges© 2016 Pearson Education, Inc.

Chapter Review of Learning Outcomes

• Can you describe the characteristics of a scientific hypothesis?

• Can you compare and contrast the terms scientific hypothesis and scientific theory?

• Can you distinguish between inductive and deductive reasoning?

• Can you explain why the truth of a hypothesis cannot be proven conclusively via deductive reasoning?

• Can you describe the features of a controlled experiment, and explain how these experiments eliminate alternative hypotheses for the results?


Chapter Review of Learning Outcomes

• Can you list strategies for minimizing bias when designing experiments?

• Can you define correlation, and explain the benefits and limitations of using this technique to test hypotheses?

• Can you describe the information that statistical tests provide?

• Can you compare and contrast primary and secondary sources?

• Can you summarize the techniques you can use to evaluate scientific information from secondary sources?
