As you learned in the lesson in this module titled "Types of Investigations," there are many types of investigations that scientists perform. We examined three types.
| Investigation Type |
Purpose | Hypothesis? | Variables manipulated? |
Control? |
| Descriptive | To draw conclusions | No (but does answer a question) | No | No |
| Comparative | To determine relationships | Yes | Yes | No |
| Experimental | To determine a causal relationship | Yes | Yes | Yes |
Look carefully at the hypothesis and variables manipulated columns. Notice that in descriptive investigations there is no hypothesis and no variables manipulated but in comparative and experimental investigations there is both a hypothesis and variables that are manipulated.
A hypothesis is a proposed explanation for an observable phenomenon. For a hypothesis to be used in science, one must be able to test it in the form of an experiment. The hypothesis is not just an “educated guess.” Hypotheses should be based on previous observations that cannot be explained with available information. A scientific investigation is designed to test this hypothesis.
In an experimental investigation, the hypothesis should establish a cause and effect relationship. The cause is the independent variable in the investigation and the effect or result is the dependent variable and is a prediction of what the student thinks will happen.
In a comparative experiment, the hypothesis should identify the relationship between the independent and dependent variable. Often the hypothesis of a comparative experiment identifies which level or condition of the independent variable will perform the best when the dependent variable is applied.
The basic form of a hypothesis is usually similar to one of the following: