The model year of a vehicle and the amount of miles it has been driven

Question

What is the correl between the year of the car and the miles drive? Is it positiv, negative or no correlation

Answer 1

If you were to graph the data from a random sample of, say, 50 cars, you could use the x-axis to record the model year of each car, and the y-axis to record the mileage reading from each car. Let's say your oldest car is a 1930 model, and its mileage is 175,000. And suppose your newest car is a 2018 model, and it has only 200 miles driven on it so far. The coordinates of the oldest car would be (1930, 175,000) and the coordinates of the newest car would be (2018, 200). Now draw a line from the first pair of coordinates to the last pair. Is that line sloping up to the right, or down to the right? If it slopes upward to the right, it is a positive correlation; if it slopes downward to the right, then it is a negative correlation. If you were to add the remaining coordinates for the other 48 cars, do you think that, in general, the older the car, the more miles it's been driven? If so, then the "best-fit" line for all your coordinates would have the same sign (+ or - ) slope as your line between the oldest & newest cars.