The Scientific Method

I. The scientific method is an orderly way to solve problems

• Five steps:– 1. Observations/Asking a question– 2. hypothesis– 3. Experiment– 4. Recording results– 5. Discussion & Conclusion

A. Asking a question- Based on identification of a problem

- Scientists make OBJECTIVE observations of the natural world in order to identify the problem.

- Observations are followed by inferences, logical interpretation based on prior knowledge and experience.

B. Hypothesis – possible explanation for a set of observations

• Making an “educated guess” that is testable.

• Deductive hypothesis: “if”…”then” statement.

• Inductive hypothesis: most common type; gut feeling.

C. Designing an Experiment:• Controlled experiment – only one

variable, or factor, is changed at a time.

• All other factors are called constants and are exactly the same for all test groups.

• Independent variable – the thing that is changed or manipulated.

• Dependent variable – the response to the change that was made. (What you measure)

Controlled experiment• Based on a comparison of a control

group and an experimental group.

• Control group – the “norm” – you don’t do anything to this group. It should represent the normal situation, and be a standard of comparison.

• Experimental Groups – these are the groups that you change or manipulate to test a certain variable.

• Example: You are testing a certain drug was effective in lowering blood pressure:

• All participants in the study should be similar in age/gender/condition to eliminate these factors from affecting the results. You only want to test ONE FACTOR or VARIABLE at a time.

• Control group: People who receive a PLACEBO (or a pill that doesn’t do anything). These people have not received treatment and can be compared to the ones who do.

• Experimental Group: People who receive the blood pressure medicine.

D. Recording data

– Qualitative data – descriptive info, such as color, texture, etc.

– Quantitative data – numerical info

– In the recording section of a scientific paper, the scientist simply RECORDS the data, they do not attempt to analyze or explain it.

– Create graphs and tables to illustrate your data

E. Discussion & Conclusion

*Explain the graphs and tables in paragraph form. – Refer back to your graphs in your

written description. • Ex. As seen in figure 1.1, the amount of

oxygen…….

*This is where you interpret your data, and tell us what it means.

Drawing Conclusions

• -explain your findings – whether you “support” or “reject” your hypothesis

F. Ideal Experiments

• Should be repeatable.

• Scientists publish at the end of the process, so that others may share their knowledge and verify their results.

G. Theories vs. Laws• Theory

– Attempts to explain WHY something happens

– Applies to a well-tested explanation– Unifies a broad range of observations– Is subject to change - Ex.: atomic

theory

• Law– Always true– Explains WHAT happens– Ex. Law of gravity

II. Real-life example:

• 1976 – outbreak of disease in Zaire, Africa

• Disease was very contagious and deadly

• Victims had severe headaches, fever, bloody diarrhea, and vomiting.

In the last stages of the disease:

• Victim’s internal organs bled uncontrolably and blood leaked through the nose, ears, and even skin.

• Death from shock and cardiovascular shock followed rapidly.

What happened?

• Teams of scientists from the Centers for Disease Control were sent to Zaire to investigate what seemed to be a new disease.

Centers for Disease Control (CDC)

• Agency for the United States government responsible for monitoring diseases.

• The CDC is also the agency in charge of dealing with bioterrorism.

A. OBSERVATION

• All scientific understanding of the world starts with an observation or question about something unusual or unexplained.

• For example: People are dying from

a disease that no one has seen before.

Here are some of the initial data/observations the CDC recorded:• Outbreak had caused nearly 300 deaths

• Death followed within a week of 1st symptom

• 80 to 90% of people who become infected died.

• Photographed a virus in the blood of victims

• Observations always lead to the formation of a question:

• What is this new disease?

• How is it transmitted?

• What is the disease causing agent???

(I.e. – is it a bacteria, virus, parasite…)

B. CDC hypothesis:

• CDC scientists believed that a virus they had photographed in the blood of victims was the organism that caused the disease.

To test a hypothesis, scientists make a prediction that logically follows from the hypothesis:

• For example: If the virus were the true disease-causing agent, then introducing the virus into healthy tissue would cause cell death like that found in victims of the disease.

C. EBOLA EXPERIMENT• Liver cells from a monkey were placed

in a test tube (monkeys are genetically similar to humans)

• Test tubes in the control group (the

group that mimics NORMAL environment) were left alone.

• Blood containing the virus was placed in the experimental test tubes.

• Independent variable – the addition of blood to the monkey cells.

• Dependent variable – the health of the cells.

D. Collecting data:

• 11 days after addition of virus blood – the experimental group cells were dead.

• Control group was fine.

• Liquid from the experimental group could be passed to healthy cells, resulting in rapid death.

E. Conclusion:

• The virus photographed was the infectious agent. (caused the disease)

• In a conclusion you admit the failings of your experiment: – for example: scientists still don’t

know the animal that harbors the virus in the wild – or how the virus is spread to humans.

• Scientists also don’t know how EBOLA virus is spread –

– They know it requires close contact

– Don’t know if the person has to have a break in the skin to get the virus.

Hemorrhagic = bleeding

The scientific method is a cycle:

Observation

question hypothesis

prediction

experiment

Collect data

Analyze dataconclude

(revise hypothesis if necessary.)