Buy a Car With Data - Part 2

14 February 2012

In our previous blog post we identified 27 cars based on a list of features, and then narrowed our list down to 3 based on Internet data and test drives. Now, it is time for more data!

Deep Dive

With a list of cars this small, we can do more in-depth research. We found out the cost of car insurance, average maintenance costs, vehicle crash ratings, accident data, and insurance data. We also tried to estimate how much each model would cost to own over 5 and 10 years.

However, the most interesting data was about crash test ratings and accident statistics. Vehicle crash-test ratings are designed to be predictive, which means they try to imitate real-world conditions. Accident data is far more interesting, because it shows what actually happened.

The Honda Civic accident data suggests it is less safe than a Fit or Prius. We eliminated it from our list. You can’t argue with data.

We are left with 2 options: the Prius and the Fit. It is time to look at specific cars for sale.

Round 3: Specific Cars

The Internet makes it easy to find data. In our case, we used and to get a list of cars within 200 miles of Seattle. We wanted to find any Prius or Fit for less than $20,000 and with under 60K miles. We found 105 cars. Now that we had data, it was time for analysis!


Our biggest question was how to consider several variables. Which is better: a $15,000 car with 32,000 miles or a $12,000 car with 46,000 miles? What if one is a year older than the other?

The way we handled this is by focusing on the variables that mattered the most to us: price, mileage, and age. We created a ‘score’ for each car’s variable, from 0% to 100%. 100% meant it was the best deal. 0 mean it was the worst. For example, the car with the lowest mileage had a ‘mileage score’ of 100%.

To find a ‘Good Deal Score’, we weighted the different scores, and then added them. We said that price matters 50%, mileage 16.6%, age 16.6%, and warranties 16.6%.

You can see the results below. The best cars had a good deal score of over 5. You can see how the best scores are often given to cars with low mileage and a low price.

Learn About Tableau

We looked at the top 2 Priuses and Fits, sorting by their Good Deal Score. We realized that the 2009 Prius for $15,000 and with 25,000 miles was what we wanted. We called the car dealer, had them email us the final price ($16.5K with sales tax and registration), and we bought the car that day. No pressure, no hassle, and we knew we got a great deal. Success!


Lessons Learned:



What We Wish We Had: