The UK Reliability index takes into account all factors of a repair, the cost of the parts and the frequency of failures - The Average of all cars is 100 which means that if the figure for the car you are looking at has a higher than average index (118) it indicates that that car is less reliable than the average, if however there is a lower than average index (60) the reliability is better.

Separately to this figure you can also look at the average cost of repairs for a particular make or model, a car with a good reliability index and a high average cost would imply that the frequency of failure is low, however when it does fail the bill will be a lot more than the average. Toyota, for example, has a high average cost of repair but quite a good index rating - which means that the car fails infrequently but when it does you will be in for a larger than average bill. Overall however, Toyota is a very strong make of car to buy.