In This Chapter

Brushing up on the scientific method

Analyzing scientific investigations

Evaluating and applying scientific theories and laws

In an attempt to understand and explain natural phenomena, scientists engage in inquiries that involve asking questions, making observations, formulating hypotheses (educated guesses), conducting experiments to test hypotheses, analyzing results, asking more questions, and so on. To keep themselves honest and obtain the most accurate information possible, they follow a specific procedure when conducting these inquiries, called the scientific method.

On the GED Science test, you’re likely to encounter a few questions that test your understanding of the scientific method, so in this chapter, we explain the basics and provide sample test questions for practice.

Getting a Bird’s-Eye View of the Scientific Method

The scientific method is a step-by-step approach to answering science questions and solving problems. It ensures the credibility and reproducibility of experimental evidence.

Now you’d think that for a scientific method to be scientific, all scientists would agree on the steps involved. They sort of do agree, but if you search online for “scientific method,” you’ll find a variety of scientific methods (plural). Our version of the scientific method goes like this, with a couple loops, as shown in Figure 6-1:

Observe and wonder. Many of the most important scientific discoveries start with an observation — information obtained primarily through the senses (seeing, hearing, touching, and so on). Alexander Fleming discovered penicillin when he was cleaning up petri dishes in his lab and noticed that around the edges of a patch of mold growing in one of the dishes, infectious staph bacteria had been killed. He wondered, “Why?”
Research. Another scientist may have answered the question or solved the problem already. Research provides insight into what’s already been done to answer the question or solve the problem. The research may show that plenty of work has been done and the question or problem remains.
Formulate a hypothesis. A hypothesis is a proposed explanation for a condition or occurrence that can be tested and either proved or disproved. A hypothesis can usually be phrased as an if/then question; for example, “If you warm a cup of water, it will dissolve more sugar.”
Define variables and controls. Establishing variables and controls is the first step toward designing an experiment:
- Variables: Conditions that are changed to determine the effects of those changes. In the water/sugar example, heat is the variable being changed.
- Controls: Conditions that remain unchanged, to prevent them from influencing the results. In the water/sugar example, using water from the same source and making sure the same amount of water is used for each test are controls.
Create a procedure. A procedure is a step-by-step process for conducting the experiment or study, including specifics about the data that will be collected and how it will be recorded.

The procedure is very important because it enables other researchers to evaluate the process used to create and gather data. If the experiment or study is done right, anyone should be able to follow the same steps and get the same results. A poorly designed experiment or study produces unreliable data.
List and gather the required materials. Before starting an experiment or study of any sort, the scientist needs to gather all the supplies needed, including, in some cases, participants for the experiment or study.
Conduct the experiment or study. It’s show time! Scientists conduct the experiment or study and record the results.
Analyze the data. Analysis can be as simple as looking at the data or it may involve plugging it into a spreadsheet, rearranging it, using it to create graphs, and so on.
Draw conclusions or not. The results may lead to certain conclusions, may be inconclusive, or may bring up other questions that need to be answered first. In some cases, the conclusions reveal a problem in the design of the experiment or study or the way it was performed.

*John Wiley & Sons, Inc.*

Figure 6-1: The scientific method.

Certain steps in the scientific method may vary slightly. For example, if a scientist stumbles on something very unusual, research may not be necessary. The scientist can skip ahead to the hypothesis and then plan an experiment to test it. Likewise, if the results of an experiment are inconclusive, the scientist doesn’t necessarily jump back to hypothesis. She may be able to trace the reason for the inconclusive results to a problem in the variables and controls, the procedure followed, the materials used, mistakes in conducting the experiment, or the analysis. In addition, sometimes results lead to observations that may take the scientist down another path.

1. example A scientist traveling in Kenya has suffered terribly with nasal allergies for decades. He discovers a group of people who don’t have any allergies. Most of the people are infected with hookworm. He hypothesizes that hookworms may cure his allergies, so he introduces the parasite into his system. Which step(s) in the scientific method did he skip?

(A) observation, research, and hypothesis

(B) research and variables and controls

(D) hypothesis, variables and controls, procedure, and materials

2. Janice is testing two different fertilizers to see which works better. She uses Fertilizer A on the vegetable garden in her backyard and Fertilizer B on her flower garden in the front of her house. The plants in the vegetable garden grow three times faster and larger than the plants in her flower garden. She concludes that Fertilizer A is the better product. What is wrong with the design of Janice’s experiment?

(A) It has no well-defined variables.

(B) She did not propose a hypothesis.

(D) Janice forgot to do her research.

3. Patsy Sherman, a chemist at 3M, was working on developing a rubber substance that would not deteriorate when exposed to jet aircraft fuels. She mistakenly splashed some on her shoe and noticed several weeks later that the areas on her shoe that had the substance on them looked nearly new, while areas without the substance were dirty and stained. She assumed the substance must have been responsible for preserving the shoe. To confirm her suspicions, Patsy needed to conduct

(A) research

(B) experiments

(D) analysis

4. After gathering results and conducting a thorough analysis, a scientist concludes that the results are inconclusive. Which step should he go back to in the process?

(A) research

(B) hypothesis

(D) it depends

Now check your answers:

The scientist made an observation and a hypothesis, so you can eliminate Choices (A), (C), and (D). Choice (B) is the only correct answer. The scientist did no research and didn’t establish variables and controls. He tested only on himself, so his results are likely to be unreliable. If his allergies disappear, he may want to find more participants for his next experiment, assuming he can find people to volunteer to be infected with hookworm.
The problem is that Janice failed to use controls, Choice (C). To perform a controlled experiment, every factor other than the fertilizer needs to be the same in the two groups being tested. The two fertilizers would need to be tested on the same plant type, growing in the same soil with the same amount of sunshine and water.
Patsy would need to conduct controlled experiments, Choice (B), to determine whether the substance or something else was responsible for protecting her shoe. Choice (A) is a good second choice, but because Patsy was the chemist developing the substance, she would probably have little or no research available to help her.
It depends, Choice (D). In most cases, scientists can revise the hypothesis and start over from that point. However, if the scientist can pin down the reason for the inconclusive results and attribute it to a problem in the design or execution of the experiment, she can go back to that point in the process instead of having to return to almost the beginning.

Evaluating the Design of Scientific Investigations

When science people, including medical professionals, read and publish studies, they’re concerned not only with the results of a scientific investigation but also with the methods followed, which include everything from how participants are chosen to the number of participants, the length of the study, and even whether the people conducting the study may have a biased perspective. For example, when prescription medications are tested, the researchers are generally required to disclose whether they have any financial ties to the pharmaceutical company that manufactures the medication, so that anyone evaluating the study can take that into consideration.

Finding and eliminating sources of error

If scientists were perfect, then every experiment would prove the hypothesis and be reproducible by any other scientist at any time. Unfortunately, scientists are human, and errors may creep into the observations, leading to results that can’t be reproduced. In a proper and valid experiment, all errors and potential errors should be documented and analyzed to help researchers in the future reproduce the experiments without repeating the errors. Errors are generally divided into two groups:

Systematic errors: Flaws in the experimental procedure from faulty calibration of measuring instruments, faulty use or reading of an instrument (parallax error), using faulty equipment, or using equipment that was designed for some other purpose. Properly documenting systematic errors helps future researchers avoid them.

Systematic errors are typically one-sided errors (consistently high or consistently low).
Random errors: These arise when those conducting the experiment have trouble reading measurements; for example, when a needle moves when taking a reading or a needle is between two lines on a meter. Such errors affect measurement precision and can be reduced through repeating the measurement or refining the measurement method or technique.
Random errors are typically two-sided errors (results fluctuate above and below the true or accepted value).

1. example Why is documenting errors in experiments or studies so important?

(A) It enables researchers to repeat the experiment without repeating the errors.

(B) Any error can affect the conclusions reached.

(D) All of the above.

2. Why is the documentation of errors in an experiment important for consumers, as well as for scientists?

(A) Attorneys can use the information to sue drug companies.

(B) You may want to become a scientist one day.

(D) Consumers may want to conduct the studies themselves.

3. Scientists record the procedures they followed to conduct an experiment for which of the following reasons?

(A) to enable others to evaluate the experiment and its conclusions

(B) to inform the scientific community of recent discoveries

(D) to encourage other scientists to reproduce the experiment

Check your answers:

All the answer choices, Choice (D), explain why documenting errors in an experiment is important.
Scientists aren’t the only ones who need to evaluate the reliability of data from studies. Consumers, Choice (C), can also benefit from knowing about errors in studies.
Disclosing the procedures followed enables others to evaluate the experiment and its conclusions, Choice (A).

Identifying the strengths and weaknesses of a scientific investigation

Scientific investigations should be empirical; that is, conclusions should be based on verifiable observation, experience, and experimental evidence. For a scientific investigation to produce reliable results, it must meet all the following criteria:

Participants/subjects must be chosen randomly.
Controls must be in place to reduce or eliminate variables not being tested.
Only one variable can be manipulated and tested. (More than one may be used, but that makes statistical analysis difficult.)
Results must be quantifiable — size, number, weight, or something else that can be measured. For example, the number of hairs on a cat is quantifiable, although they would be very difficult to count, whereas the softness of the cat would be qualitative — a judgment call, unless you could figure out some way to quantify it.
Participants/subjects must be assigned randomly to either the experimental or control group.
Participants/subjects may also be retested, so they’re tested in both the experimental and the control group. This “repeated measure” technique produces more uniform results. When repeated measures are done, counterbalancing may also be done to reduce the effects of the order in which participants are tested in either the experimental or control group.
All evidence must be reported, even if — and perhaps especially if — it doesn’t support the hypothesis. If evidence is excluded, the reason for the exclusion must be provided.

Controls are particularly important. When pharmaceutical companies conduct tests on medications, they commonly use the following three types of controls:

Control group: A group that establishes a baseline from which results are measured. The control group receives no treatment or a neutral treatment. Results from the treated and untreated (control) groups are compared to determine whether treatment had any effect.
Placebo: Untreated participants in a study often respond differently if they think they received treatment. To account for this placebo effect, researchers provide a neutral treatment (such as a “sugar pill”) that has no real effect.
Blinding: Those conducting the study hide the fact that some participants are receiving a placebo and some aren’t, because when people know they’re getting a placebo, they’re less likely to respond to it. In a double-blind test, neither the researcher nor the participant is aware of who’s getting the placebo, so nobody involved can inadvertently influence the results by what they say or do.

Another factor that determines the quality of a scientific study is its size. A study that involves a large number of experiments, participants, or measurements is likely to produce a more accurate body of data than does a smaller study. When testing products, researchers often refer to each experiment as a trial.

1. example The number of variables that should be changed in a properly designed and well-controlled experiment is

(A) 0

(B) 1

(D) depends on what is being tested

2. When planning and conducting an experiment, one should

(A) carefully choose participants

(B) test as many variables as possible

(D) try to prove the hypothesis

3. Which of the following evidence should be reported in the results of a scientific study?

(A) results from only one selected trial

(B) results from only those trials that prove the hypothesis

(D) results from all trials

4. Which of the following is not quantifiable data?

(A) beauty

(B) height

(D) speed

example Read the following excerpt from “Science Fair Fun: Designing Environmental Science Projects for Students Grades 6–8” (www.epa.gov/osw/education/pdfs/sciencefair.pdf) and write a short response to the prompt that follows it.

Give your project a title

Choose a title that describes what you are investigating. Make it catchy, yet descriptive.

State the purpose of your project

Ask yourself: “What do I want to find out? Why am I designing this project?” Write a statement that answers these questions.

Develop a hypothesis

Make a list of answers to the questions you have. This can be a list of statements describing how or why you think the subject of your experiment works. The hypothesis must be stated in a way that will allow it to be tested by an experiment.

Design an experiment to test your hypothesis

Make a step-by-step list of what you will do to test the hypothesis. Define your variables, the conditions that you control or in which you can observe changes. The list is called an experimental method or procedure.

Obtain materials and equipment

Make a list of items you need to perform the experiment. Try to use everyday, household items. If you need special equipment, ask your teacher for assistance. Local colleges or businesses might be able to loan materials to you.

Perform the experiment and record data

Conduct the experiment and record all measurements made, such as quantity, length, or time.

Record observations

Record all your observations while conducting your experiment. Observations can be written descriptions of what you noticed during an experiment or the problems encountered. You can also photograph or make a video of your experiment to create a visual record of what you observe. Keep careful notes of everything you do and everything that happens. Observations are valuable when drawing conclusions and are useful for identifying experimental errors.

Do calculations

Perform any calculations that are necessary to turn the data from your experiment into numbers you can use to draw conclusions. These numbers may also help you make tables or graphs summarizing your data.

Summarize results

Look at your experimental data and observations to summarize what happened. This summary could be a table of numerical data, graphs, or a written statement of what occurred during your experiment.

Draw conclusions

Use your results to determine whether your hypothesis is correct. Now is the time to review your experiment and determine what you learned.

Document your findings in a report, display, and presentation

Record your experiment and the results in a report, a display, and, if required, a presentation. Your report should thoroughly document your project from start to finish. If you can choose the report format, it should include a title; background or introduction and purpose; hypothesis; materials and methods; data and results; conclusions; acknowledgement of people who helped; and bibliography. You may want to prepare a poster or three-dimensional display to give your audience an overview of your project. You can use charts, diagrams, or illustrations to explain the information. Bring a computer with a slide show or video of your experiment and the results. Your display should include a descriptive title; photos, charts, or other visual aids to describe the project and the results; the hypothesis; and a project report near the display.

Some science fairs require oral presentations. In preparing your presentation, ask yourself, “What is most interesting about my project, what will people want to know about, and how can I best communicate this information?” Use an outline or note cards to help you in your presentation. Be sure to check the rules for the presentation. You will probably need to introduce yourself and your topic; state what your investigation attempted to discover or prove; describe your procedure, results, and conclusions; and acknowledge anyone who helped you. Practice your presentation before delivering it.

Use this checklist to help you walk through the steps to a good science fair project:

Select a topic.
Conduct background research and prepare a bibliography.
Formulate a testable hypothesis.
Write a step-by-step experimental procedure.
Develop a list of items and equipment for the experiment.
Prepare a project schedule.
Conduct the experiment, make observations, collect data, and document everything.
Prepare visual aids (such as charts and graphs).
Develop a report outline.

Using the material in the preceding passage, write a short response to the following prompt:

Why would students benefit from doing a science project following the procedure of the scientific method?

This question should take you about 10 minutes to complete.

Ask a friend or a family member to read your response to determine whether you’ve answered the prompt in sufficient detail, citing evidence from the passage. Your response should be written in proper English in an acceptable essay style with no spelling or grammatical errors.

Interpreting independent and dependent variables

Variables are anything that changes during the course of an experiment, and they come in the following two varieties:

Independent: An independent variable is the condition that the researcher chooses to change. If you’re testing how temperature affects pressure in a pressure cooker, the temperature of the water is the independent variable that you manipulate.
Dependent: A dependent variable is the result from manipulation of the independent variable. If you crank up the temperature of water in a pressure cooker, the dependent variable is the pressure, which rises accordingly.

For example, suppose a scientist designs an experiment to test how high different quantities of helium will lift his cat into the air. He buys balloons, string, helium, and a suitable harness for his cat. He ties the harness to his cat and starts filling the helium balloons and tying them to the harness. In this case, the independent variable is the amount of helium, and the dependent variable is the height his cat is lifted off the ground.

Here are some other examples of dependent and independent variables in scientific experiments.

Digging into Scientific Theories and Supporting Evidence

The general public often dismisses scientific theories as irrelevant hunches that scientists have. In the world of science, however, a theory is an interpretation of the facts. Although the theory is subject to change, it’s not a willy-nilly guess. So when you see something like the “Big Bang theory” or the “theory of global warming,” you can rest assured that scientists have invested a great deal of study, thought, and debate in coming up with that particular theory. Think of hypotheses, theories, and laws as a hierarchy of truth:

Hypothesis: An explanation of a limited number of observations based on experience, background knowledge, and logic.
Theory: An explanation of a wide range of observations presented in a concise, coherent, systematic, predictive, and broadly applicable statement. A theory explains why a certain thing or condition is the way it is. A theory can’t be considered to have been proven by the results of a single experiment. Repeated experimentation makes the conclusions reached more acceptable and credible.
Law: An explanation of a wide range of observations that will most likely not be proven wrong. A law is less likely than a theory to be proven wrong. However, a law doesn’t necessarily describe why something is the way it is. A law is more useful at predicting outcomes. For example, Newton’s laws of motion don’t explain how forces work but do provide a practical means for making calculations related to mass and force.

Any theory that has been proven repeatedly with consistent results may become a scientific law until disproven, in which case its status returns to that of a theory. Advances in equipment leading to more accurate measurement can lead to this change in status.

You may also hear the term model, which is a concept that has some validity and can be used to formulate predictions that are accurate only under certain limited conditions. Meteorologists often use different models to predict the weather.

Science can be described as an ongoing debate between evidence and conclusions. As new evidence is discovered, it may challenge or add support to conclusions that were previously made or even to well-established theories.

In the following sections, we explain how to determine whether evidence supports or challenges a theory; how to apply scientific models, theories, and processes; and how to apply formulas that have been developed from scientific theories.

Determining whether evidence supports or challenges a theory or conclusion

You can read about challenges to scientific theories in the news. Nearly every day, someone challenges the theory of global warming, questioning whether Earth really is heating up, whether the problem really is related to the amount of carbon in the atmosphere, and whether human activities really are the primary cause. And perhaps that theory itself will continue to evolve as technological advances reveal more about ecology and the effects of the potential life of living, breathing creatures on Earth.

However, many people dismiss theories more out of ignorance than anything else. Global warming skeptics, for example, point out that Earth has experienced numerous cycles of warming and cooling over its 4.5 billion years of existence, failing to recognize that the current warming trend doesn’t follow the same pattern as those other cycles. We’re not saying that all global warming skeptics are ignorant. We’re just saying that if you’re going to question or challenge a theory or conclusion, you need solid evidence to dispute it. Scientist are pursuing various avenues through their experiments to disprove or prove the theories.

On the test, you may encounter questions that involve making a judgment call on whether evidence supports or challenges a theory or conclusion or what theory or conclusion can be drawn from a particular data set.

1. example Which of the following pieces of evidence does not support the conclusion that H. pylori bacterium causes peptic ulcers in humans?

(A) Nine out of every 10 participants in a study who were infected with H. pylori bacterium developed peptic ulcers.

(B) Antibiotics that kill H. pylori bacterium have proven 90 percent effective in treating peptic ulcers.

(D) Thirty to fifty percent of the population is infected with the H. pylori bacterium.

2. Which conclusion can be drawn from the following data?

Sugar Consumption (% of calories)	Increase in Systolic Blood Pressure (mm Hg)
10	0.0
20	2.0
30	6.2
40	10.4

(A) Increased sugar consumption raises blood pressure.

(B) People should stop consuming sugar.

(D) Results are inconclusive.

3. Medical researchers are beginning to believe that cholesterol-lowering medications used to treat patients with heart disease may cause dementia. Which of the following pieces of evidence would provide the best support for this conclusion?

(A) Several doctors reported that patients of theirs who had been prescribed cholesterol-lowering medication suddenly developed problems with thinking and memory.

(B) A double-blind, placebo-controlled study involving 200 participants demonstrated cognitive decline in patients taking a cholesterol-lowering medication.

(D) In several trials, rats given high doses of cholesterol-lowering medications developed cognitive difficulties, as measured by their performance in navigating complex mazes.

Check your answers:

The fact that a certain percentage of the population is infected with H. pylori bacterium, Choice (D), doesn’t mean that it causes peptic ulcers. If you chose Choice (A), (B), or (C), then you are confusing correlation with causation.
The higher the percentage of calories from sugar, the higher the blood pressure, so Choice (A) is the correct answer.
A well-controlled study, Choice (B), provides better evidence than clinical evidence from doctors, Choice (A), or patients, Choice (C). Choice (D) represents good evidence, but the fact that high doses of medications cause a certain side effect in rats doesn’t necessarily mean that a standard dose of the medication in humans will cause the same side effect.

Applying scientific models, theories, and laws

While evidence may support or challenge a scientific theory, you can go the other way and use scientific models and theories to explain natural phenomena and to predict the outcome of certain experiments or natural occurrences. On the test, questions may challenge your ability to apply scientific models and theories.

Using formulas from scientific theories and laws

Scientists often develop mathematical formulas to describe natural phenomena. Scientific theories and laws provide formulas that have a wide range of uses in fields ranging from engineering to medicine. Engineers, for example, apply the formulas to design buildings and machines that actually do what they’re expected to do and to perform calculations that enable great accomplishments, such as landing people on the moon and land rovers on Mars.

Ohm’s law is an example. It states that the current through a conductor between two points is directly proportional to the difference across the two points to arrive at the mathematical formula that describes this relationship: images where V is the voltage, I is the amperage, and R is the resistance. To answer questions on the test that involve formulas such as this, you don’t need to memorize the formulas. The test presents the formula to use, and you just need to figure out which numbers to plug in and how to do the math.

Analyzing Experimental Design and Scientific Theories

Getting a Bird’s-Eye View of the Scientific Method

Evaluating the Design of Scientific Investigations

Finding and eliminating sources of error

Identifying the strengths and weaknesses of a scientific investigation

Give your project a title

State the purpose of your project

Develop a hypothesis

Design an experiment to test your hypothesis

Obtain materials and equipment

Perform the experiment and record data

Record observations

Do calculations

Summarize results

Draw conclusions

Document your findings in a report, display, and presentation

Interpreting independent and dependent variables

Digging into Scientific Theories and Supporting Evidence

Determining whether evidence supports or challenges a theory or conclusion

Applying scientific models, theories, and laws

Using formulas from scientific theories and laws