The Index is formed by Manufacturer and also by type/model. This ensures that no individual poorly or highly performing model can unduly influence a manufacturer's overall Index figure.
All that particular manufacturer's ratings added up into one figure that should expose whether cars from this stable are generally reliable - or maybe not! Perhaps most models lack in a certain area, Audis suspensions might be a case in point. Any manufacturer can introduce the occasional misfit but this rating might give you the confidence to consider a later model edition or an alternative model from the same marque - or satisfy your general misgivings and encourage you to look elsewhere!
Depending on your vehicle these can make you rue the day you bought it or hopefully give you a warm glow! Find out how your present or potential car lines up against its competitors in key reliability areas - the lower the figure the better the reliability, the higher the figure the more the likelihood of frequent or costly repairs.