What are the confounding variables?

What are the confounding variables?

A variable that is not considered but plays a role in the outcome of an event is considered a confounding factor.
ref:https://medium.com/hackernoon/what-is-a-confounding-factor-6f30487de3e9
ref:https://www.youtube.com/watch?v=1Cn1smM3kbQ

A confounding variable is something that is correlated with both your independent and dependent variable, but that you left out of your analysis.

For example, you are investigating hours spent studying for a class and grade in the class. But it turns out there are hard classes, where people study a lot and grades are low, and easy classes, where people don’t study much and grades are high. Therefore, you wrongly conclude that studying leads to lower grades.

The correlation does not have to be causal, it might just happen that way. For example, you’re investigating whether a drug helps people get over colds faster. You hand out the drug to 100 people with colds, and also track 100 other people with colds who do not get the drug. But by chance, you gave the drug to 80 people with common colds and 20 people with more serious flu, while the control group had 80 people with flu and 20 people with colds. You conclude that the drug works great, but it might have just been that it was given to a population that was going to get better sooner anyway.