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How our Expert Rating scores are calculated

Our Expert Rating index is now the gold standard for rating and ranking new cars in the UK

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There are dozens and dozens of automotive websites in the UK, and most of them include reviews of new cars. All up, there are tens of thousands of UK car reviews on the internet.

So how do you decide whose opinion to believe when you’re looking for a new car? Is Auto Express better than Autocar? How does the Telegraph compare to the Sunday Times? Or what about The Car Expert and Honest John? All of their reviews are written by experienced journalists, but they’re still all human beings with their own preferences and biases.

Not only that, but every website has its own way of measuring and scoring cars. If you’re only relying on one source, you’re not getting the full picture.

Fortunately, we’re here to help with our unique Expert Rating index.

What is an Expert Rating?

The Expert Rating score for a car is an aggregated rating made up of a number of individual review scores from up to 35 different sources. This can be as few as 12 reviews and in some cases is more than 60 (as some cars have multiple variants of engines, body styles and trim levels).

The world’s most famous review aggregator website is Rotten Tomatoes, which compiles reviews for movies and TV shows. It then rates them on the number of positive reviews vs negative reviews, but there are many different methods of aggregating scores.

The Car Expert is the first website to successfully apply review aggregating to new car reviews. Our system uses a “weighted average” of all the reviews of a particular car published by the 35 sites we include in our index. This is a similar process to sites like Metacritic (another film/TV/music review aggregator site), although we have our own proprietary algorithm developed specifically for new car reviews.

A weighted average is more complicated than a straight average (which is what we used to use) because there are additional factors we take into consideration.

We factor in the age of each review, so that newer reviews carry more weight than older reviews, and we normalise the scores from each title to account for variations in the scoring systems they each use.

The Expert Rating index also breaks down the complex web of different scoring systems that different websites use in their reviews. A score of 7 out of 10 from one site might be an above average score from one site, a fairly average score from another site and below average from yet another site. So how is the average car buyer supposed to know which site to trust? The Expert Rating index pulls all of that data together and makes hundreds of calculations to produce an updated score – the only number that you can trust.

It’s taken us a couple of years to develop and test the calculations to make sure they work, which is why we’ve only recently shifted from a simple average to our weighted average system.

It’s no understatement to say that this is now the gold standard for rating and ranking new cars in the UK.

Our Expert Rating index is now the gold standard for rating and ranking new cars in the UK.

How can you justify that claim?

Rather than one person’s opinion or one website’s view on what makes a car good or bad, we compile and analyse new car reviews from 35 of the top UK motoring websites. Then we apply a complex set of calculations to bring you the definitive rating for every new car.

Our advanced Expert Rating algorithm factors in the age of the review and the scoring methods used by all 35 different sites. Every day, it recalculates and updates the Expert Rating score for every single car. The scores for every car can shift every time a new review for any car is added to the database.

For car buyers, it’s an easy-to-use guide to all the key information on each new car. You can see, at a glance, what each website has said about a car, and click on a link to visit that site and read the full review. We also include complete Euro NCAP safety ratings, Green NCAP eco ratings and a list of any awards the car has won.

So far, we have published more than 500 new car ratings and we’re adding more each week. Our database contains more than 15,000 individual reviews and is growing daily. We currently track 35 automotive titles and we’re currently reviewing additional sites with a view to expanding that number to 40.


How do you calculate the Expert Ratings?

The Expert Rating score is an aggregated rating made up of a number of individual review scores. Unless it’s a very niche model, we usually require a minimum of 12 scored reviews before we include a car in our Expert Rating Index. Some cars have more than 60 reviews used in our calculations.

When we launched the Expert Rating Index in 2019, we used a simple average of all the review scores to determine the Expert Rating score. While this was much better than relying on any one single score, it had limitations based on aggregating reviews from different sites with very different scoring systems and methodologies. So we developed version 2.0, which rolled out in 2021.

The current Expert Rating score for a car uses a “weighted average” of all the reviews of a that model published by the 35 sites we include in the Index. We factor in the age of each review (newer reviews carry more weight than older reviews) and we normalise the scores from each publication to account for variations in how they each score their reviews.

We are currently working on the next major update to the Expert Rating Index, which is exponentially more sophisticated again and should roll out in early 2024. More details very soon…

So how exactly are the scores weighted?

Sorry, that information is classified Ultra Top Secret and is above your security clearance.

What we can tell you is that it’s a complex mathematical algorithm applied universally to all media titles in the Index. We don’t manually alter any individual review scores, but every review is automatically fed through our super-secret algorithm.

What about car reviews that don’t provide a score?

Some titles review a lot of cars but they don’t provide scores (like the Daily Mail and the Sun). Other titles won’t score reviews for a short test and will only score vehicles on longer reviews. These reviews are still added to the database so you can find them and read them, but they don’t count towards the Expert Rating score.

Unlike some aggregator sites (Metacritic is one example), we don’t manually alter scores up or down, or create scores for unscored reviews. That works for their system, but we don’t think it’s the right solution for us. Occasionally, however, we may include a review but not its score if we think that it is not a fair representation. This decision is made solely by our editor.

That car’s score has changed twice in the last month. Why is that?

It’s perfectly normal for Expert Rating scores to shift up or down over time, and there are a few reasons for that happening.

Firstly, we are constantly adding new reviews to our database. For a new model launch, the big sites (Auto Express, Autocar et al) tend to get first crack, then the secondary sites. Finally, niche sites and regional titles get to review the cars. This process can take months. Then there will be additional versions (new engines, new trim levels) and facelifts, so the whole process repeats itself again and again. We will publish an Expert Rating once we have about 12 reviews in our database, but we may end up with 50 or more reviews over the production life of a vehicle.

Secondly, some sources will adjust their reviews scores over time. This may be as cars are re-evaluated against newer rivals, or it may be for a specific reason. For example, the 2021 Dacia Sandero was originally given quite high scores from most sources – right up until Euro NCAP crash-tested the Sandero and gave it a very poor two-star score. Several sites immediately downgraded their scores accordingly (and, in one embarrassing case, had to revoke a ‘Car of the Year’ award…).

Thirdly, the reviews are weighted for age. Older reviews carry less weight than newer reviews, which means the overall score is more influenced by newer reviews. Usually (but not always), a car’s rating will gradually decrease over the course of its production cycle as it slowly goes from being the hottest new model on the block to being old and outdated at the end of its life.

Finally, our advanced algorithm automatically accounts for any changes in scoring scales or methodology from any of our sources.

Oh, and one more thing after the final thing. In 2022 we introduced a different algorithm for used cars, which is currently applied to models that are no longer on sale. We have big plans to expand this in 2024, so keep checking back for the latest information.

Which publications contribute towards the Expert Ratings?

We started out tracking 12 sites, concentrating on the largest and best-known automotive publications that review the most cars. Over the last four years, we have broadened that out to a current total of 35 carefully selected sites, including national newspaper sites that have substantial and regular motoring content. We have also added a few specialist titles that target specific areas of the new car market (green cars, fleet buyers, performance cars).

As of November 2023, the list is:
Auto Express, Auto Trader, Autocar, Business Car, Car, Car Keys, Carbuyer, Carwow, Company Car Today, Daily Mail, Daily Mirror, Discover EV, Driving Electric, Electrifying, Eurekar, Evo, Fleetworld, Green Car Guide, Heycar, Honest John, Motoring Research, Motors.co.uk, Move Electric, Parkers, RAC, The Car Expert, The Intercooler, The Scotsman, The Sun, The Sunday Times, The Telegraph, Top Gear, What Car?, Which?, and Which EV?

Why have you selected those sites?

We have a range of criteria for inclusion, but mainly we’re looking at the quality and quantity of reviews. We also consider the variety of cars reviewed by each publication and how the reviews are scored. We only take websites into account, rather than printed titles, so we can always link back to the original review source.

We also review our existing sites periodically and could remove some sites from the Index if we don’t think they are contributing sufficiently to warrant their ongoing inclusion. Our next review is set for early 2024, when we will decide whether to add any new sites and/or remove any existing ones from our calculations. Any future expansion is dependent on review quality rather than simply adding more sources for the sake of it.

We only use UK sites in our Expert Rating Index, although many of the reviews are conducted in Europe or other parts of the world as part of a new model’s global press launch. A car’s pricing and specification can vary dramatically around the world, so a review from a US or European website won’t necessarily reflect that car’s position in the UK market.

Does anyone else use your rating technology?

Our aggregated ratings are available to licence. The data is already being used by Leasing.com, one of the UK’s leading leasing comparison sites. Leasing.com’s ratings are powered by the same review data as our own Expert Rating Index, but we run them through a bespoke algorithm to provide a unique set of scores.

If you would like to enquire about licensing our ratings, please email editor@thecarexpert.co.uk.

How often are the Expert Ratings updated?

We’re updating information in the Expert Rating Index daily, although that doesn’t mean we update every car every day. On average, each car will be updated about once a month so the information is about as current as you’ll see anywhere.

How do you decide which cars to add to the Index?

We have almost every new car on sale and we’re working as fast as we can to get the rest. Currently, there are only a few niche models not currently listed.

Broadly speaking, we’ve tried to get all of the most popular cars included as a priority. In other words, there are more Fords and Fiats than Ferraris.

We’re also adding more used cars to the Expert Rating Index, since 90% of all households buy used cars rather than new. Getting quality data from older models is tricky, as there are fewer sources available. We also use a slightly different algorithm for used cars.

How do you separate different versions of the same car?

It can get tricky deciding whether to lump different versions of a model together or rate them separately. We look at this on a case-by-case basis.

For example, the Audi A4 has a multitude of different variants. We include the saloon, Avant (estate), A4 allroad and S4 versions all under the one general umbrella of “Audi A4”. But the Audi RS 4 is considered separately because it’s a very different vehicle.

Similarly, we consider electric models separately from petrol/diesel/hybrid models. A good example is the Vauxhall Corsa (petrol/diesel) and the Vauxhall Corsa Electric.

Do you factor in Euro NCAP scores?

No, they are separate. We only use the overall review scores from each title. In many cases, these scores specifically take Euro NCAP safety ratings into account, so the Euro NCAP rating is indirectly included anyway. For example, Which? will heavily mark down any car with a Euro NCAP score of three stars or worse.

Do you include owners’ reviews from any of the sites?

No, we don’t count user reviews even though some of the sites we track display owners’ ratings or carry out owner surveys (like the annual Auto Express Driver Power survey).

Owner reviews have some good points, but they can also be problematic. Most of the time, owner surveys are completed by people who’ve just bought a new car and are still in love with it, or by those who have had a bit of a nightmare and want to vent about it. This tends to create a very polarised data set of very good and very bad reviews, rather than balanced and objective opinions that encompass a range of scores. You see the same thing across the internet in almost all situations – just look at Amazon for a good example.

Owner reviews are also much harder to verify and easier for PR departments (or salespeople, Russian bots, MI6…) to influence, whereas reviews from recognised media sources and journalists are more reliable and trustworthy.

We are investigating ways of aggregating different user reviews to create an overall Owner Rating score to sit alongside the Expert Rating score, but so far we have found the data to be too sporadic and unreliable to provide a valuable score that readers can trust.

Can you add my site to the Expert Rating Index?

We are currently evaluating additional websites for inclusion in our Expert Rating Index. We have a range of criteria for inclusion, but mainly we’re looking at the quality and quantity of reviews, the variety of cars reviewed and how the reviews are scored. We only take websites into account, rather than printed titles, so we can always link back to the original review source.

We also review our existing sites periodically and could remove some sites from the Index if we don’t think they are contributing sufficiently to warrant their ongoing inclusion.

If you would like your site to be considered for inclusion in our Index, please email editor@thecarexpert.co.uk.

How to read our Expert Ratings information

Expert Rating

Our unique Expert Rating is calculated by compiling new car review scores from across all the top UK automotive media titles, rather than just our own opinions. This means you get a balanced view of multiple opinions from up to 35 different sources, with links back to all the original articles so you can read them for yourself.

Safety Rating

We list the full Euro NCAP safety ratings for each model, rather than just the headline score. This includes a complete breakdown of scores for adults, children, pedestrians and assist systems, so you can see the information that matters most to you. We also highlight any scores that have expired.

Euro NCAP scores expire after six or seven years, as the scoring criteria gets tougher each year and cars that were tested several years ago can no longer be guaranteed of maintaining their initial score. A car may be re-tested if it’s still on sale, although this doesn’t always happen.

Eco Rating

We include the new Green NCAP eco ratings for each car where they are available, including air quality and energy efficiency ratings for each model and engine tested. This programme only started in February 2019 and was paused in 2020 as a result of the Covid pandemic, so there are relatively few models listed so far, but this will hopefully grow quickly.

Reliability Rating

We include reliability data from one of our commercial partners, MotorEasy. This is taken directly from MotorEasy’s network of service centres, both from franchised dealers and independent garages. We look at warranty claims for each model, assessing both the number of claims and the average cost of the claims.

MotorEasy also provides reliability data to many other sources, such as the What Car? Reliability Award.

Running Costs Rating

We take running cost data from our technical partner, Clear Vehicle Data. Analysing millions of data points, we provide average scores across a model range for the biggest expenses when running a car. These are:

  • fuel consumption
  • CO2 emissions (which affects road tax and other charges)
  • insurance group (a crucial factor in your annual car insurance premium)
  • servicing, maintenenace and repair costs (covering the first five years)

Clear Vehicle Data also provides running cost data to many of the UK’s top leasing and fleet companies.

Security Rating

We have security ratings for several new cars as tested by Thatcham Research, which assess the theft risk of new cars. This includes theft by relay attack for keyless entry/keyless start systems.

The programme started in 2019 but was discontinued in 2021, so very few cars display a security rating. We still display this information as it’s useful for potential customers, but no new additions to the Index will have a security rating.

Thatcham Research is also the UK’s member of Euro NCAP. Along with sister organisations in other European countries, it conducts many crash tests and other assessments for Euro NCAP ratings each year.

Last updated: 16 November 2023

Stuart Masson
Stuart Massonhttps://www.thecarexpert.co.uk/
Stuart is the Editorial Director of our suite of sites: The Car Expert, The Van Expert and The Truck Expert. Originally from Australia, Stuart has had a passion for cars and the automotive industry for over thirty years. He spent a decade in automotive retail, and now works tirelessly to help car buyers by providing independent and impartial advice.