In a descriptive investigation, the purpose is to draw conclusions about something or describe it. Since it is essentially a learning process about something, it is typically used when the researchers know little about the subject matter. It poses a question to be answered but does not typically include a hypothesis. Keywords to look for when identifying a descriptive investigation include describe, identify, observe, and list.
An example of a descriptive investigation would be students learning basic information about rock formation. The student may ask, “how do plutonic rocks form beneath the Earth’s surface?” The experiment process would then include research of the topic, data collection from this research, and some type of conclusion drawn from the investigative process. The student would learn that molten rock from the Earth’s mantle can erupt from a volcano and force the hot, liquid magma onto the earth’s surface where it cools and becomes solid volcanic rock. With little prior knowledge of the subject matter, the student isn’t likely to pose a hypothesis in a descriptive study, but can ultimately answer a question utilizing this type of investigation.
In a comparative investigation, the purpose is to compare/contrast the relationship between two things. Keywords to look for when identifying a comparative relationship include categorize, compare and contrast, or differentiate between.
While a comparative investigation typically includes components of the scientific inquiry such as observations and a scientific question, it also includes a hypothesis, unlike the descriptive investigation. Since it compares two systems, or two populations, or two conditions to one another, the researcher generally has some basic knowledge that leads them to believe one has an edge over the other. This knowledge is what prompts the experiment.
For instance, one spring day, you park your car under a tree mid-morning. When you go to leave for lunch, you notice your car is a bit chilly. The next day, you park your car in an open area, exposed to sunlight. When you leave for lunch, you feel the car is warm. This observation leads you to compare the difference in temperatures at the same time between point A (under the tree) and point B (an open area, uninhabited by shade trees). Another example is you notice the pH of the water in your family pond changes following a heavy rain. You might consider the effects of rain on the pH level by measuring it before and after the rain.
The difference between a comparative relationship investigation and an experimental investigation is the presence of a control group. Since a control group is defined as a group within the experiment that doesn’t receive treatment by the researchers, we can see that this does not apply to the experiments mentioned above, nor is a control group necessary in either scenario to accurately address the posed questions.
Finally, in experimental investigations, the same components of the descriptive and comparative investigations are included: a purpose or posed question, a hypothesis, and independent/dependent variables. But this type of investigation also includes a control group. This type of investigation revolves around the design of an unbiased and fair experiment in which variables are manipulated and controlled to gather evidence which either supports or rejects your hypothesis.
For instance, someone plants a strawberry plant that never produces any strawberries. The following year, they plant it in a different location that receives more sunlight and it produces some strawberries. They then form the hypothesis that “a strawberry plant will produce more fruit when routinely exposed to more hours of sunlight.” Ultimately, this individual is studying the relationship between the sun and a strawberry plant and investigating if sunlight exposure plays a role in fruit production.
These types of experiments have a definite independent and dependent variable. So, for the strawberry plant example, the plant itself is your dependent variable. The sun is the independent variable. The plant may or may not be dependent on the sunlight. To incorporate the control within this experiment, you can place the strawberry plant in an area where it receives an average amount of sunlight per day. So, your control may be a strawberry plant exposed to an average of 4-6 hours of sunlight daily. The variable of sunlight exposure is then controlled by having a strawberry plant sitting on a dark porch, unexposed to any sunlight. The third strawberry plant is exposed to 6-8+ hours of sunlight daily.
In an experimental investigation, every other identified variable must be held constant to deduce that the sunlight is the only variable manipulating the outcome of the experiment. So, it would be imperative to make sure all three strawberry plants were being watered at the same times, with the same amount of water. If fertilizer is utilized, all 3 plants should receive the same amount of fertilizer, at the same frequency and at the same time. All 3 strawberry plants must be the same brand, or grown in the same setting, and planted in the same type of soil. To accurately produce an experimental investigation, the researcher must identify all variables and control all of them but one, in this case, sunlight.