1. Chapter 1
Introduction to the Scientific Method Can Science Cure the Common Cold?

2. 1.1 The Process of Science
Science is not a giant collection of facts to be memorized.
Process, using the scientific method:
Observing
Proposing ideas
Testing
Discarding those ideas that fail

3. 1.1 The Process of Science The Nature of Hypotheses
Hypothesis: proposed explanation
Testable and potentially falsifiable
Where do hypotheses come from?

4. 1.1 The Process of Science The Nature of Hypotheses
Both logical and creative influences are used
Chance
Logic
Intuition
Experience
Previous scientific
results
Imagination
HYPOTHESIS
Scientific theory
OBSERVATION
QUESTION
Figure 1.1

5. 1.1 The Process of Science Scientific Theory
Powerful, broad explanation of a large set of observations
Rests on many hypotheses that have been tested
Generates additional hypotheses

6. 1.1 The Process of Science The Logic of Hypothesis Tests
Example: consuming vitamin C decreases the risk of catching a cold
Inductive reasoning: combining a series of specific observations into a generalization

7. 1.1 The Process of Science The Logic of Hypothesis Tests
To test, make a prediction using deductive reasoning.
Involves using general principle to predict an expected observation
“if…then” statement

8. (that is testable and fasifiable)
1.1 The Process of Science
The Logic of Hypothesis Tests
The process looks something like this:
Hypothesis
(that is testable and fasifiable)
Consuming vitamin C reduces
the risk of catching a cold.
Make prediction
If vitamin C decreases the risk
of catching a cold, then people
who take vitamin C
supplements will experience
fewer colds than people
who do not.
Test prediction
Conduct experiment or survey
to compare number of colds
in people who do and do not
take vitamin C supplements.
Figure 1.3

9. 1.1 The Process of Science Figure 1.3 (continued) If people who
take vitamin C
suffer fewer
colds than
those who do
not. . .
If people who
take vitamin C
suffer the
same number
of colds or
more than
those who do
not. . .
Conclude that
prediction is
true
Conclude that
prediction is
false
Do not reject
Reject the
the hypothesis
hypothesis
Conduct
additional
tests
Consider
alternative
hypotheses
Figure 1.3 (continued)

10. 1.1 The Process of Science The Logic of Hypothesis Tests
A hypothesis that fails our test is rejected and considered disproven.
A hypothesis that passes is supported, but not proven.
Why not? An alternative hypothesis might be the real explanation.

11. 1.2 Hypothesis Testing
The most powerful way to test hypotheses: do experiments

12. 1.2 Hypothesis Testing
Experiments support the hypothesis that the common cold is caused by a virus.
(a) Cold–causing virus
(b) How the virus causes a cold
Nasal
passages
Host cell
Throat 1
Virus
Virus introduces its
genetic material into a
host cell.
Protein
shell
Genetic
material and
proteins 2
The viral genetic material instructs the
host cell to make new copies of the
virus. Immune system cells target
infected host cells. Side effects are
increased mucus production and throat
irritation.
Virus
copies 3
Immune
system cells
New copies of the virus are
released, killing host cell. These
copies can infect other cells in
the same person or cells in
another person (for example, if
transmitted by a sneeze).
Released
virus
copies
Mucus
Figure 1.4

13. 1.2 Hypothesis Testing The Experimental Method
Experiments are contrived situations.
Variables: factors that can change in value under different conditions
Independent variables can be manipulated by the scientist
Dependent variables cannot be changed by the researcher

14. 1.2 Hypothesis Testing Controlled Experiments
Controlled experiment: tests the effect of a single variable
Control: a subject who is not exposed to the experimental treatment
Differences can be attributed to the experimental treatment.

15. 1.2 Hypothesis Testing Controlled Experiments
Example: Echinacea tea experiment:
Hypothesis: drinking Echinacea tea relieves cold symptoms
Experimental group drinks Echinacea tea 5-6 times daily.
Control group drinks “sham” Echinacea tea (placebo).
Both groups rated the effectiveness of their treatment on relieving cold symptoms.

16. 1.2 Hypothesis Testing Controlled Experiments
People who received echinacea tea felt that it was 33% more effective at reducing symptoms.
Figure 1.7

17. 1.2 Hypothesis Testing Minimizing Bias in Experimental Design
If human subjects know whether they have received the real treatment or a placebo, they may be biased.
Blind experiment: subjects don’t know what kind of treatment they have received
Double blinding: the person administering the treatments also doesn’t know until after the experiment is over
“gold standard” for experimentation

18. 1.2 Hypothesis Testing Using Correlation to Test Hypotheses
It is not always possible or ethical to experiment on humans.
Using existing data, is there a correlation between variables?

19. 1.2 Hypothesis Testing Using Correlation to Test Hypotheses
Hypothesis: stress makes people more susceptible to catching a cold
Is there a correlation between stress and the number of colds people have caught?

20. 1.2 Hypothesis Testing Using Correlation to Test Hypotheses
Results of such a study: the number of colds increases as stress levels increase.
Figure 1.10

21. 1.2 Hypothesis Testing Using Correlation to Test Hypotheses
Caution! Correlation does not imply causation.
The correlation might be due to other reasons.

22. 1.2 Hypothesis Testing Using Correlation to Test Hypotheses
Figure 1.11

23. 1.3 Understanding Statistics
Overview: What Statistical Tests Can Tell Us
We can extend the results from small samples to an entire population.
Difference between two samples: real or due to chance?

24. 1.3 Understanding Statistics
The Problem of Sampling Error
Sampling error: the effect of chance
We can calculate the probability that a result is simply due to sampling error.
Statistically significant: an observed difference is probably not due to sampling error

25. 1.3 Understanding Statistics
The Problem of Sampling Error
Confidence interval: the range of values from a sample that has a 95% probability of containing the true population mean (average).
Much population variation = large confidence interval
Small population variation = small confidence interval

26. 1.3 Understanding Statistics
Factors that Influence Statistical Significance
Sample size
The true difference between populations
Bigger is better: more likely to detect differences

27. 1.3 Understanding Statistics
Factors that Influence Statistical Significance
Figure 1.15

28. 1.3 Understanding Statistics
What Statistical Tests Cannot Tell Us
If an experiment was designed and carried out properly
Evaluate the probability of sampling error, not observer error
May not be of any biological significance

29. 1.4 Evaluating Scientific Information
Primary Sources
Researchers can submit a paper about their results to a professional journal (primary source).
Peer review: evaluation of submitted papers by other experts
Secondary sources: books, news reports, the internet, and advertisements

30. 1.4 Evaluating Scientific Information
Information from Anecdotes
Anecdotal evidence is based on one person’s experience, not on experimental data.
Example: a testimonial from a celebrity

31. 1.4 Evaluating Scientific Information
Science in the News
Secondary sources may be missing critical information or report the information incorrectly.
Consider the source of media reports.

32. 1.4 Evaluating Scientific Information
Science in the News
Be careful with the internet since anyone can post information.
Be very cautious about claims made in paid advertisements.

33. 1.4 Evaluating Scientific Information
Understanding Science from Secondary Sources
Use your understanding of the process of science to evaluate science stories.
News media generally highlight only those science stories that seem newsworthy.
They are more likely to report a positive result than a negative one.

34. 1.5 Is There a Cure for the Common Cold?
No, but prevention methods are known.
Wash your hands!
No effect on cold susceptibility:
Vitamin C
Exposure to cold temperatures
Exercise
No vaccine for the common cold