Overview of the Scientific Process

Transcription

1 The purposes of this lab exercise are to: Overview of the Scientific Process 1. Introduce you to the LabPro3 system, one of the tools we will use in future lab exercises, and which you may choose to use for your research project, and 2. Provide you with an opportunity to work in small groups on a common question, using the scientific method. 3. Produce data that can be used to introduce the use of analytical software in the lab. The scientific method is a way of answering questions about relationships, such as cause and effect, and solving problems in a logical way (deductive reasoning), most often through experimentation. This method has three main steps, providing the guidelines necessary for the clear communication of ideas, procedures and conclusions throughout the scientific community. I. Observation II. Hypothesis III. Testing Observation Observation is arguably the most important skill in the process of science, and one of the most difficult to develop. The challenge is to build and develop confidence in your ability to observe and record accurately the relevant information, as well as all of the recognized and potential influences on a particular observation. It is from these carefully recorded observations that scientists discover questions or problems suitable to scientific investigation. However, while one may raise an array of interesting or important questions, not all questions are answerable by the scientific method. For example: Do higher environmental temperatures cause people to act in an immoral way? (imagine a 102 degree day in downtown New York) Are dogs happier when you feed them steak? In addition, the nature of some questions limits the ability of researchers to demonstate a cause and effect relationship, and instead scientific methods may only be able to support a trend or a correlation. For example: Was the lung cancer in a 70 year old man caused by his 45 year smoking habit? Below are some questions to which the scientific method has been applied successfully. In what way(s) are these questions different from the ones above? Why is grass green? What is the cause of AIDS? How does penicillin kill bacteria? Is calcium necessary for growth? 1

2 When you begin to formulate a question, make sure it is answerable by the scientific method. In other words, the topics of scientific investigation must be: 1) well-defined 2) measurable 3) controllable Once you are satisfied with your question or problem, you then formulate a hypothesis. Hypothesis The hypothesis is a possible explanation or answer to your question/problem, based on relevant data and your trained judgement. The primary challenge is to develop a reasonable hypothesis that has the potential to be proven false. As part of the experimental design, two alternate predictions of the outcome are set forward. More specifically, a null hypothesis predicts that a condition (or treatment) will have no effect or that there will be no difference between conditions (treatments). It anticipates that nothing will change. The null hypothesis is tested by your experiment, designed with the potential to reject this null hypothesis. For example: Null hypothesis: Dietary calcium will have no effect on growth. The alternative hypothesis states that there will be an effect as a result of treatment (continuing with the same example): Alternative hypothesis: Dietary calcium has an effect on growth. If your null hypothesis is rejected as a result of your experimental findings, you must then tentatively accept the alternative hypothesis. Remember, you can not prove a hypothesis true using the scientific method, but rather you describe evidence that enables you to discredit or support a hypothesis. Testing I. Determine the variables: 1. Independent variable(s) The independent variable is the condition which is manipulated by the researcher or which is allowed to change naturally. The researcher chooses the independent variable ( treatment ) that he/she believes will affect the dependent variable. This relationship is predicted in the hypothesis. Examples of potential independent variables selected in tests of human physiology include: amount or type of food, drug level (eg. caffeine), and time. For your research project in this class, I recommend that you choose only one independent variable. 2. Dependent variable(s) The dependent variable is the condition that changes and which is measured/recorded. Choose the dependent variable(s) most important to answering the question within the framework of the hypothesis. Once identified, the researcher must determine the most appropriate method of measurement. For example, if growth is identified as the dependent variable, in what way should growth be measured? Total height, weight, surface area, bone length, bone density, time to reproductive maturity, etc., could all be valid measures of growth. Generally, the method that is the most simple and most reliable (having the least chance of measurement error) is selected. 2

3 3. Controlled variables Controlled variables are always potential independent variables which are held constant so as to isolate the effects of the chosen independent variable. Design your experiment carefully so that any changes in the dependent variable can be attributed to the independent variable. For example, if you were to study the effects of coffee intake on heart rate, you would control for all of the other factors which might effect heart rate: activity level, time of day, age, etc. How is this different from a control treatment? II. Design the procedure Often, procedures are adopted from previous research or developed as new technology is made available. Look in the literature for possible suggestions and talk with others who have experience in that area of research, but feel free to be creative. Keep in mind, however, that experimental methods must be reproducible by other investigators. I have attempted to make this step as straight-forward as possible for you, by providing a form in your packet for you to complete. You must make decisions concerning each of the following elements: 1. Population of Interest Who will your test subjects be, and how many are necessary for your particular analysis? How many subjects do you need, for example, to calculate an average, or to identify a trend? 2. Levels of treatment What is the appropriate range of the independent variable relevant to your hypothesis? 3. Control treatment In order to compare the predicted effects of experimental treatment, is it appropriate to include a test where the independent variable is eliminated or kept at a standard value? (What would the control treatment be in an experiment which tests the effect of different types of exercise on muscle strength?) 4. Number of replications There is inherent variablity among test subjects, especially humans (not everyone will respond in exactly the same way). How many times should you repeat the experiment in order to be confident that your sample data accurately represents the whole population? 5. Error Look for and record areas with a potential for introducing error into your results, and then reduce this potential by modifying your experimental design. I recommend that you construct data tables and graphs of predicted results before you begin to collect real data. This insures that you are familiar with the methods and will help you trouble-shoot your design before you invest serious time and effort. III. Analyze and present data Once collected, the data is organized and summarized in order to 1) determine whether the hypothesis is supported or rejected, and 2) for clarity in presenting your results to the scientific community. (See the separate handout on writing the scientific paper.) Tables are generally used to present averages and other results of statistical analysis. DO NOT include raw data in a scientific report. Figures (graphs) are best used to compare results from more than two treatments, to demonstrate or compare trends, or to make predictions about treatment levels not 3

4 tested. Captions are placed above tables; for graphs, they go below. The independent variable in your experiment is displayed on the x-axis, and the dependent variable on the y-axis. Each axis of a graph must be labeled and include the unit of measure. Formulate and report only those conclusions that are directly related to your hypothesis and experimental design. In other words, the scientific paper is not an appropriate place to make guesses about what might have happened if.... Further, if your analysis leads you to reject your alternative hypothesis, do so clearly and without reservation. Support or rejection of an hypothesis are equally valuable conclusions to research. You can, however, critique your experimental methods and offer improvements which might better answer the original question. Summary Use your curiosity, experience, and observations to ask a good question. Propose an explanation in the form of a testable hypothesis (null and alternative hypotheses). Determine the components of the experiment. Make predictions based on possible experimental outcomes. Then design the best possible experiment (including method of analysis), making revisions as needed BEFORE you begin to collect the experimental data. Lab Exercise: In groups of 4-5, the class will use the scientific method to design a simple experiment using the Vernier system in order to answer the same question. Each individual group, however, will have to determine and agree upon their own definitions and methods. You should follow the research proposal form included on the next page, your notes on the scientific method, and the Vernier System instructions. Your group should test at least 5 subjects. (This means everyone in the class will serve as a test subject at least once, and likely more than once. You should allow at least 15 minutes recovery time between tests.) I recommend that you construct a table in which to record your results (item 7 on the proposal form). I expect that each group will design a slightly different experiment in their effort to answer the common question. Differences will likely be found in: the definition of the test population, the definition of recovery from exercise, the hypothesis, and predicted outcomes. As a direct result, I hope that you will experience the creative aspects of the scientific method, and in general, the attention to detail required in designing and executing an experiment that will produce the best answer to your question. Question: How does heart rate and respiratory rate change during recovery from exercise? Materials: The following materials/equipment are available for you to choose from. Please inquire about the availability of any other materials you believe are necessary to conduct your experiment. Step stools Metronomes Hand grip Heart rate sensor unit Spirometer sensor unit 4

5 Instructions for HR data collection with Lab Pro 3: 1. Connect the receiver module of the Heart Rate Monitor to the Vernier computer interface. 2. Open the file 04 Heart Rate and Exercise from the Human Physiology with Vernier folder. 3. Set up the Heart Rate Monitor. Follow the directions for your type of Heart Rate Monitor. Using a Hand-Grip Heart Rate Monitor a. Grasp the handles of the Hand-Grip Heart Rate Monitor. Place the fingertips of each hand on the reference areas of the handles (see Figure 1). b. The left hand grip and the receiver are both marked with an alignment arrow. When collecting data, be sure that the arrow labels on each of these devices are in alignment (see Figure 2) and that they are not too far apart. The reception range of the plug-in receiver is cm, or about 3 feet. 4. Stand quietly facing your table or lab bench. 5. Click to begin data collection. There will be a 15 s delay while data are collected before the first point is plotted on the upper graph. Thereafter, a point will be plotted every 5 s. 6. Determine that the sensor is functioning correctly. The readings should be consistent and within the normal range of the individual, usually between 55 and 90 beats per minute. If readings are stable, click and continue to the next step. 7. Click to begin data collection. If the baseline appears stable, begin to exercise for the duration determined in your experimental design. Record the maximum HR. 8. When the exercise phase is completed, stand in place while your heart rate slows toward its resting pre-exercise value. Data will be collected for 200 s. 9. Click and drag over the area of the graph where the resting heart rate is displayed. This will highlight the region of interest. 10. Click the Statistics button,. Record the mean resting heart rate. Figure Drag the right hand bracket to the right edge of the graph, until all the data points are highlighted. The values in the Statistics box will be adjusted based on the data within the brackets. Record the maximum heart rate. 12. Move the statistics brackets to highlight the area of the graph beginning with the maximum heart rate and ending with the first data point that matches the initial baseline value (or the last point graphed, if baseline is not achieved). Record the Δx value displayed at the lower left corner of the graph as the recovery time. 5

6 Instructions for Respiratory Rate data collection with Lab Pro 3: 1. Connect the Spirometer to the Vernier computer interface. Open the file 20 Respiratory Response from the Human Physiology with Vernier folder. 2. Attach the larger diameter side of the disposable bacterial filter to the Inlet side of the Spirometer head. Attach a disposable Spirometer mouthpiece to the other end of the bacterial filter (Figure 2). 3. Hold the Spirometer in one or both hands. Brace your arm(s) against a solid surface, such as a table, and click to zero the sensor. Note: The Spirometer must be held straight up and down (as in Figure 2) during data collection. 4. Collect inhalation and exhalation data. Figure 2 a. Put on the nose plug. b. Click to begin data collection. c. Taking normal breaths, begin data collection with an inhalation and continue to breathe in and out. After 4 cycles of normal inspirations and expirations begin your exercise for the pre-determined duration. d. After exercise, stand quietly. Continue to breathe into the Spirometer. Data will be collected for 120 s. 5. Click the Next Page button,, to see the volume data. If the baseline on your graph has drifted, use the Baseline Adjustment feature to bring the baseline volumes closer to zero. 6. Select a representative peak and valley in the portion of your graph prior to the onset of exercise. Place the cursor on the peak and click and drag down to the valley that follows it. Record the Δy value displayed in the lower left corner of the graph to the nearest 0.1 L as before exercise tidal Volume. 7. Select two adjacent peaks in the portion of your graph prior to the onset of exercise. Click and drag the cursor from one peak to the next. Use the Δx value displayed in the lower left corner of the graph to calculate the respiratory rate in breaths/minute. Record this value to the nearest 0.1 breaths/min as initial respiratory rate. 8. Repeat Steps 6 and 7 two times. The first time, select regions in the potion of your graph during exercise and the second time select regions after normal breathing had been resumed. Record the values for during and after exercise. 9. Calculate the Minute Ventilation values for before, during, and after exercise. (Tidal Volume) X (Respiration Rate) = Minute Ventilation 6

7 Group Research Proposal Names: Lab Day: Question: How does heart rate and respiratory rate change during recovery from exercise? Project Title: Null Hypothesis: Alternative Hypothesis: Description of Experimental Design: 1. What are the dependent, independent and controlled variables? 2. Describe the test population (including # of student test subjects), the levels of treatment, # of replications, and control treatments. 3. What do you need in terms of equipment or supplies? 4. How will the experiment be performed? (outline the steps) 5. What is the time line (what will happen first, second...etc, and how much time do you require to complete the experiment)? 6. What do you predict will happen as a result of your experimental treatment? (expand on your alternative hypothesis) 7. What will your recorded results look like (give some hypothetical examples) and how will you present your results? (be specific) 8. How will you analyze your results (statistics)? 7