Recall, the Scientific Method is hypothesis-driven; one makes an educated guess to explain a cause-and-effect relationship. Experiments are conducted to test this guess and ultimately answer if the hypothesis is true or false (there is no right or wrong).
Design is different from the Scientific Method. Design is needs-driven with the goal of optimally designing something to meet some demand. For instance, you don't hypothesize about constructing artificial hearts but design and construct systems that increase a patient's quality of life. Design often leads to hypothesis-driven research. A design's performance begs questions: Why did it fail or why does it perform so well? Without educated guesses and experimental verfication, one doesnt' know.
Briefly the Scientific Method (i.e. hypothesis-driven research) involves Observation, Hypothesis, Controlled Experiment and Conclusion. More specifically:
You notice something, and wonder why it happens. You see something and wonder what causes it. You want to know how or why something works. You ask questions about what you have observed. You want to investigate. The first step is to clearly write down exactly what you have observed.
Find out about what you want to investigate. Read books, magazines or ask professionals to learn about the effect or area of study. Keep track of where you got your information from.
Choose a title that describes the effect or thing you are investigating. The title should be short and summarize what the investigation will deal with.
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other. At this point, you are ready to translate your questions into hypothesis. A hypothesis is a question which has been reworded into a form that can be tested by an experiment.
Make a list of your answers to the questions you have. This can be a list of statements describing how or why you think the observed things work. These questions must be framed in terms of the variables you have identified. There is usually one hypothesis for each question you have. You must do at least one experiment to test each hypothesis. This is a very important step.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure or specific aims.
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments. It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did. Other things you can mention in the conclusion
The problem: your friend's car doesn't start
The process of Observation, Hypothesis, Controlled Experiment and Conclusion would involve the following:
You don't see any oil spots on the ground. Externally the car looks fine. You don't smell any gasoline odors. However when you turn the key you hear clicking sounds but the car's engine doesn't start.
Your friend tells you he filled the car with gas. What other facts would you gather?
In addition to gasoline and spark plugs, a working car battery, fuses, an alternator are all needed to start the car's engine. If one or more of these variables fail, then the engine won't start.
At this point you make an educated guess. The variables you identified above must be examined one at a time (perhaps it's a dead battery AND a blown fuse).
A hypothesis is a question
which has been reworded into a form that can be tested by
Your hypothesis can be phrased like
My guess is (fill in the blank) is the reason for (fill in the blank)
Potential hypotheses for the car not starting are:
At this point, you must carefully weigh your resources and available time. Suppose your guess is the bad battery. Are you willing to spend time going to the store, paying a $100 for a battery and replace the one you suspect to be dead? If the car still didn't start, what can you absolutely conclude? Maybe the sales person sold you a defective battery and that's why the car still doesn't start.
The problem is that you don't have any preliminary data. For example, measuring battery voltages from several cars with working batteries, versus cars that don't start because of bad batteries, helps establish ground truth and perhaps some trend. You are now in a position to design additional experiments to test your hypothesis. Rather than running to the store and going through all the trouble of buying a new battery, carefully thought out experiments save time, effort and money.
You want to avoid a look-and-see approach. Remember, you want to make an educated guess - your "best" bet. Otherwise your tests are just check lists that you pseudo-randomly select. Much time, money and energy can be wasted by doing this random search!
My hypothesis, based on my initial observations and discussions with my friend (who says his car battery is only 3 months old, but he did install new powerful speakers for his car's radio the day before) is that the fuses are blown.
Some experiments can involve the following:
Recall, a hypothesis is either TRUE or FALSE. Suppose you found the fuses were good. You've discovered, by experimentally testing your hypothesis, that it's not the fuses that's preventing the car from starting. At this point, you attempt to make another "best" guess... you don't randomly try another variable because it can waste time, money and efforts.