Ruby is conducting an investigation. an advantage of her design is that she can use a large range of variables, but a disadvantage is that it she cannot be sure that one variable is the cause of another. what kind of investigation is ruby most likely conducting?

The kind of investigation that Ruby is most likely conducting is COMPARATIVE INVESTIGATION.
There are three basic types of scientific investigation, these are: experimental, descriptive and comparative. A  comparative scientific investigation is one that involves collection of large data set from different sources under different conditions. In this type of investigation, the data collected are addressed based on the differences and the similarities among them.