What happens to your phone battery when you are using it a lot?
Negative correlation, causal relationship
Practice makes perfect
We want to find out if the amount of time spent talking on a cell phone is correlated to the remaining battery life. Let's pay close attention to this situation.
Is There a Correlation?
When we use your phone a lot, the battery dies faster than if we leave it untouched for that same amount of time. Therefore, if we are talking on the phone, the battery will lose more of its charge the longer we spend talking. A line of fit that matches this situation would be likely to resemble the graph below.
Notice that the domain can only be values within the first quadrant. We cannot talk for a negative number of minutes and we cannot continue talking after the phone battery has been fully drained. As we talk, the battery life is being drained. This is a negative correlation.
Is the Relationship Causal?
The phone usage is the reason why the battery life decreases, so the relationship is causal.
