Scientific Method - Case Studies
What is Science?
We learned from class discussion that science is a way of learning or a body of knowledge based on evidence. The learning often involves explaining an observation (a hypothesis) and then testing the explanation (an experiment). We also learned that scientists publish their work in peer-reviewed journals.
In this exercise you will choose one of the case studies below and investigate the observation further. You will propose a testable hypothesis that explains the observation, test the hypothesis by performing an experiment, and "publish" your work by writing a lab report. The lab report will be in the same format that scientists use to publish their work. Online students will create a hypothesis in this module and test the hypothesis in the next module.
Choose one of the case studies below for further investigation.
Case Study 1: Recovery after Exercise
During a hiking trip in the mountains with a large group of people, Sara noticed that some of the hikers recovered much quicker during the rest stops than others and she wanted to learn why.
If your hypothesis uses the words "recovery time," you must define recovery time. This can be done most easily using heart rate or breathing rate. You can skip this step if your hypothesis uses the words "breathing rate" or "heart rate."
If your hypothesis uses the words "recovery time," then the data that you collect should be time, not beats per minute or breaths per minute.
Case Study 2: Reaction Time
On several occasions, Sara had incidents while driving that required her to "slam" on the brakes to avoid an accident. Fortunately, she was able to avoid serious accidents in all of these situations. When reflecting upon these near-accidents, she realized that these close-calls occurred more often in the evening than in the morning because her reaction time is faster in the morning than in the evening. She used a computer to measure her reaction time and confirmed that her reaction time was faster in the morning than in the evening. She wanted to learn why her reaction time is faster in the morning.
If you choose this case study, you may not conduct an experiment that requires you to drive a car.
If you choose this case study, you should be aware that a decreased reaction is a faster reaction time (short = fast).
The purpose of this exercise is to practice using scientific method to investigate one of Sara's observations. After you select a case study above, create a hypothesis that explains the observation. You may wish to create several hypotheses and then select one for further testing. Use the following information when creating your hypothesis.
Your hypothesis does not have to be true. It is perfectly acceptable to create a hypothesis that further testing shows to be false. The purpose of the experiment is to determine if the hypothesis is true or false.
Your hypothesis should be a statement, not a question. A statement can be tested but a question cannot. Some examples of possible hypotheses are:
Case study #1: It takes longer for the heart rate of cigarette smokers to return to normal after exercise than it does for nonsmokers.
NOTE- Students may not smoke cigarettes as part of this exercise. See the section on unacceptable procedures below.
Case study #2: Reaction time is decreased five minutes after consuming a snack with 10 g of sugar.
These hypotheses can be tested. They are either true or false. The data collected will either support the hypothesis or will show that it is false.
The following hypothesis is neither true nor false because it is a question:
Does lack of sleep increase the amount of recovery time needed after exercise?
It is not possible to design an experiment to show if this hypothesis is true or false.
Your hypothesis should be specific. The first hypothesis below is difficult to test because it is too general. The second one is more specific and can be easily tested.
Too general: Cigarette smoking increases recovery time.
This hypothesis is testable because it is more specific: Cigarette smoking increases the amount of recovery time needed after 5 minutes of running on a treadmill.
Design an Experiment
You would like to know if your hypothesis is true. Describe an experiment that can be conducted during class time (campus students) or at home (online students) to test the hypothesis.
Students may not use procedures that require their subjects to drive a motor vehicle, smoke, drink alcohol, or use drugs or chemicals including prescription drugs and over-the-counter drugs. If your experiment involves consumption of food or beverages, the food or beverages must be readily available in grocery stores. In addition, subjects cannot drink more than 12 ounces of any beverage or consume more than 1 serving of any food item. Students may not use any procedures that may cause physical harm or place the subjects at risk of being harmed. Procedures that are out of the ordinary may place the participant at risk and may not be used. Lab reports will not be graded if a subject smoked, drank alcohol, used drugs, used chemicals, operated a motor vehicle, consumed excessive food or beverages as described above, or used any procedure that had any amount of risk of harm.
Some Suggestions for Testing
Recovery Time (Case Study #1)
A quick way to measure the time it takes to recover is to measure the time that it takes for the heart rate or breathing rate to return to normal. For this exercise, it might be convenient to use heart rate as a way to measure recovery but you can use any measure that you would like.
If your experiment requires that the subject exercise, it might be convenient to use a stair step. Step up onto the step and then back down repeatedly at a constant rate for approximately 3 minutes. One step every two seconds (one second to step up and one second to step down) should be a sufficient rate. Alternate legs with each step. It may be helpful to practice this for a few steps before beginning.
Resting heart rate can be used as a measure of fitness level. People who are more fit have a lower resting heart rate.
Measure heart rate by counting the number of beats in 20 seconds and multiplying your result by 3. The pulse can be felt by pressing on the wrist near the base of the thumb.
Reaction Time (Case Study #2)
The Web sites listed below provide a way to measure reaction time by measuring how quick a person can click a mouse button when the screen changes.
http://www.humanbenchmark.com/tests/reactiontime/ A QR code for this site is below.
If a computer is not available, the ruler drop technique can be used to compare reaction times. If your measurements are in inches, be sure to convert them to metric measurements (cm or mm).
A number of statistical tests are available for testing your data. This is not a statistics course, so we will use only one test- a t-test. This commonly-used test calculates the probability that the mean of one group is not different than the mean of a second group. Your experimental design should therefore have two different groups- perhaps an experimental group and a control group.
The t-test assumes that the data points are independent. For most experimental designs that involve more than one person being tested, each data point entered into the test should represent one person.
If your data are times, convert them to either minutes or seconds because the spreadsheet used for the t-test must have numbers without colons. To convert your time to seconds, just multiply the number of minutes by 60 and add this to the seconds. If you prefer to convert your time to minutes, divide the number of seconds by 60 and add this to the number of minutes.
Before proceeding with your experiment, you should do one of the following:
Online students - Online students should go back to the document titled "Scientific Method, Part 1 - Creating a Hypothesis" and participate in the class discussion on that page. After you have completed your participation in the discussion and have read all of the discussion for all of the hypotheses proposed by all of the other students, and you are confident that you have created a testable hypothesis, you may conduct your experiment and write your lab report. The hypothesis discussion is due in Module 2 and the lab report is due in Module 3.
Campus students - Campus students have already received instruction on hypotheses. You should write your hypothesis and show it to your instructor before continuing. After it is approved, you may conduct your experiment and proceed with the lab report.
The links below provide instructions for writing lab reports.
The following links will be helpful for performing a t-test on your data.
Descriptive Statistics, Graphing, Statistical Analysis - Scroll down to the heading "Statistical Analysis" near the bottom.
Online students - Online students should go to the document titled "Scientific Method, Part 2 - Experiment, Publication" in Module 3 to submit their lab report and also to submit the results of their t-test.
Campus students - Campus students will submit their reports in class. Check the syllabus for due dates.