Question

Suppose you are conducting a study to compare firefly populations exposed to normal daylight/darkness conditions with firefly populations exposed to continuous light (24 hours a day). You set up two firefly colonies in a laboratory experiment. The two colonies are identical except that one colony is exposed to normal daylight/darkness conditions and the other is exposed to continuous light. Each colony is populated with the same number of mature fireflies. After 72 hours you count the number of living fireflies in each colony. Questions: a) Is this an experiment or an observational study? Explain. b) Is there a control group and a treatment group? Identify each group. c) What is the variable of interest in this study? What level of measurement is used?

Answer 1

a) This is an experiment, since one of the variables is being controlled. The light exposure is set to work 24h a day, this is done because the researcher has made a choice. In an observational study, the researcher has no control over the variables, so no changes happen with the sample groups. Some notes are taken about their behavior, but there isn't any element that is being manipulated.

b) The control group is the one in which the fireflies keep their usual routine, there aren't any changes in their environment. This is the population exposed to normal daylight/darkness. The treatment group is the one in which the fireflies live under different conditions from what they are used to, being this the ones that are exposed to continuous light 24h/day.

c) The variable of interest in this study is the rate of survival after continuous light exposure compared to natural light exposure. The level of measurement used is ratio scale, then, since the question being made with this research is "how many individuals are going to survive?". Ratio scales allow reserachers to count concrete data.