Experimental studies are used to examine causal relationships between variables.

Suppose researchers are interested to know whether caffeinated drinks affect short-term memory.

So, how is this experiment designed to test the hypothesis?

Pre-experimental design is one of the basic types of experimental design, which involves observing the participants after some intervention. The memory tests are conducted before and after consuming caffeinated beverages, and inferences are drawn.

In the true experimental design, the samples are randomly divided into two groups, and memory tests are conducted. One group is allowed to drink the caffeinated drink, and another acts as a control group, consuming only decaffeinated beverages. After both groups have consumed their beverages, memory tests are conducted to draw inferences. 

A quasi-experimental design is similar to true-experimental design, except that the samples are not randomly assigned to groups. Instead, they are free to choose either caffeinated or decaffeinated beverages.

After examining the memory scores, the researcher can draw inferences about the effect of caffeinated drinks on memory.