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Scientific Method ~ Honors

The scientific method is a process that is used to test possible answers to questions about nature empirically in ways that can be duplicated of verified. Careful observations lead to questions which are supported or refuted through experimentation and the collection of data. In the beginning steps of the scientific method observations are made, questions are posed, and a research hypothesis is formed. This is a general statement of the answer to the question and is derived by inductive reasoning. A prediction is then made based on the research hypothesis. This is deductive or “if-then” reasoning. An illustration of statements that represent inductive and deductive logic follows:

Deductive: All dogs are animals. This is a dog; therefore, this is an animal.
Inductive: Every metal I have tested expands when heated; therefore, I can expect all metals to expand when heated.

Many scientists test hypotheses by means of controlled experiments. In a controlled experiment, a researcher manipulates or changes one factor and observes other factors that change in response to the manipulated one. All other factors are controlled or kept constant throughout the experiment. There are three kinds of variables. The independent variable is the condition or event under study. The condition or event that may change due to the independent variable is the dependent variable. The variables that are kept the same are the controlled variables. Often, the factor you are manipulating (the independent variable) is stated after the after the “if” part of the hypothesis statement or prediction. The variable or factor stated after the “then” part of the statement is the dependent variable. Sometimes the best test of a hypothesis is not an actual experiment but pertinent observations. Darwin’s theory of natural selections was developed in this way. The last step in the process of the scientific method is to analyze the data and accept or reject the hypothesis. When exhaustive experiments and observations consistently support an important hypothesis, it may be elevated to the level of theory. Like hypotheses, theories may be modified or rejected over time in the light of new information and knowledge.

Scientific Method: Scenario #1

You and your lab partner have been given the assignment of growing plants at home for second semester in class. When visiting your partner’s house, you notice their plants are healthy and robust, while you are struggling to keep yours alive. A green thumb you are not! Your partner says the secret is in the regular doses of Spartan fertilizer he/she uses. The box of fertilizer boasts of plants which are 30% taller, healthier and greener. From what you have seen, you decide that Spartan fertilizer helps houseplants grow well, and you design an experiment to test this idea. You set up the experiment as follows: 25 periwinkle plants of the same size are potted in individual 6” clay pots. All pots are filled with the same mixture and quantity of soil. You then divide the 25 plants into 5 groups. You place each group on your kitchen counter equal distance from a large picture window. You water all of the plants with equal volumes of water once a week but to group 1, 15ml of fertilizer is added, to group 2, 30ml of fertilizer is added; to group 3, 45ml of fertilizer is added; to group 4, 60ml of fertilizer is added; and to group 5, no fertilizer is added (30ml of dilute fertilizer is the suggested dose). After 6 weeks of data collection your quantitative results (bases on numerical measurements) are as follows:

Mean (average) Plant Height In Centimeters (cm)

Am’t of fertilizer

0ml

15ml

30ml

45ml

60ml

0 weeks

145

150

148

151

149

6 weeks

166

180

181

179

184
Increase in Height

21

30

33

28

35

Your qualitative (descriptive) data table indicates the