1.4.1 - Confounding Variables

Randomized experiments are typically preferred over observational studies or experimental studies that lack randomization because they allow for more control. A common problem in studies without randomization is that there may be other variables influencing the results. These are known as confounding variables. A confounding variable is related to both the explanatory variable and the response variable. 

Confounding Variable

Characteristic that varies between cases and is related to both the explanatory and response variables; also known as a lurking variable or a third variable

Example: Ice Cream & Home Invasions Section

There is a positive relationship between ice cream sales and home invasions (i.e., as ice cream sales increase throughout the year so do home invasions). It is clear that increases in ice cream sales do not cause home invasions to increase, and home invasions do not cause an increase in ice cream sales. There is a third variable at play here: outdoor temperature. When the weather is warmer both ice cream sales and home invasions increase. In this case, outdoor temperature is a confounding variable because it is related to both ice cream sales and home invasions.