Consumer Reports’ Car Reliability FAQ

What is unique about Consumer Reports' survey?

Consumer Reports' auto reliability information is unique in several respects:

• We bring this data to the information marketplace with no fear or favor. Because we have no clients beyond our readers, we can report all the data, not just the autos with top results. We needn't worry about losing advertising in our magazine, so we can interpret the data with total independence.

• Our subscribers tend to be well-educated and appreciative of objective, independent research, which makes them unusually qualified to provide valuable data about their experiences.

• The sheer size of the reliability survey conducted by the Consumer Reports National Research Center enables us to look at owners' experiences with hundreds of thousands of cars. Unlike other reliability surveys, we are able to look at car models in several variants, in some cases reporting them separately by type of engine, drive types, trim lines or other classifications.

How does CR's survey compare with other reliability surveys?

The timeframes used in collecting data also differ among surveys. J.D. Power's IQS is based on the first 90 days of ownership of new vehicles only, and its VDS (Vehicle Dependability Study) is exclusively based on 3-year-old vehicles. CR's survey asks about subscribers' experiences with their vehicles over the course of the previous 12 months and, starting with 2006, Consumer Reports' survey now covers 10 model years—from brand-new models to models that are 10 years old, providing a more complete profile of the life of a model. Our Predicted Reliability, which forecasts how well a new model is likely to hold up, is based on the cumulative experiences of owners of the three latest model years.

Where is the data from?

Consumer Reports obtains its reliability data from an Annual Questionnaire that is sent to subscribers to ConsumerReports.org and Consumer Reports magazine. In all, the survey was sent to over 8 million subscribers in 2013, and we received responses on 1.1 million vehicles.

How is the survey conducted?

The Consumer Reports National Research Center conducts the survey each spring. In the questionnaire, we ask subscribers to note any problems with their cars that occurred in the past 12 months. They are asked to identify problems that they considered serious (because of cost, failure, safety, or downtime). We ask them to include problems covered by warranty, but not the ones resulting from accident damage or due solely to recall. Respondents check off problems from a list of trouble areas, ranging from the engine and transmission to climate system, brakes, electrical system, and power accessories. See the full list of trouble spots.

How current is the data?

All our reliability information is completely updated annually. We begin sending out each year's survey in the spring. By late summer, we have collected and organized responses, and we complete our analysis and update the information online by late October. The new information first appears in print in the Consumer Reports Best & Worst New Cars, on newsstands in mid-November. Subsequent auto publications, such as the New Car Buying Guide, also use this new information. In the pages of Consumer Reports, we update Predicted Reliability and Recommendations in the vehicle Ratings beginning in the road tests in the November issue. Changes to new car recommendations and predicted reliability scores by vehicle type are published in the December issue and used car results are published in the following April issue. All reliability information we publish is based on subscribers' experiences with cars in the 12-month period immediately preceding the survey.

What expertise does CR's survey staff have?

CR's Annual Questionnaire is constructed and implemented by the staff of our National Research Center. The staff of this department includes professional social scientists, some with more than 30 years of experience in constructing, conducting, and interpreting large-scale surveys. The automobile section of the survey is developed in consultation with CR's automotive engineers and statisticians to ensure that we are capturing the most important aspects of auto reliability. The data is analyzed by professional statisticians and survey analysts.

Our decisions about the construction of the survey and the analysis and interpretation of the data are continually reviewed with an eye on giving consumers the most valuable and useful information possible.

How many cars do you have information on overall?

CR's Annual Questionnaire is one of the largest scientific surveys conducted in the United States. Our 2013 survey, which was sent to subscribers of Consumer Reports magazine and to ConsumerReports.org subscribers, gave us feedback on our subscribers' experiences with 1.1 million vehicles. This high number of responses allows CR to provide the most comprehensive reliability information available to consumers.

How many samples do you have of each model?

While we do not publish information on individual sample sizes for specific models, we require a minimum of around 100 cars to publish reliability information for a model in a given model year. Our sample sizes tend to track quite closely with market sales. Individual sample sizes vary from year to year and range from a hundred to several thousand for the more popular models. A typical model has about 200 to 400 samples for each model year and engine variant.

Since we've opened the survey to subscribers of ConsumerReports.org, we have seen a substantial increase in survey responses in the past few years, so individual sample sizes have generally been on the rise, as well. This has given us sufficient sample sizes on a number of low-volume models.

What effect does having a larger sample size for some vehicles compared with others have on the validity of the reliability data?

Given an appropriate sample, the more data you have, the more statistical confidence you have in your information. A larger sample will always give more accurate information than a smaller sample (assuming, of course, that the data are valid and collected from an appropriate source).

While we require a minimum of about 100 cars to publish reliability information, most models have larger samples than that, some being as large as several thousand. We present our data primarily to allow subscribers to compare the detailed reliability histories and overall reliability for different models. While models whose scores are based on more cars are reported with greater accuracy than those based on smaller sample sizes, the way we calculate our scores has been devised to allow valid comparisons for all samples we publish, regardless of the particular sample sizes of individual models.

Where does the minimum sample size of 100 come from?

Our statisticians have determined that a minimum sample of 100 is sufficient to allow us to report statistically-meaningful differences among models. With larger sample sizes, we could detect even finer differences among models. However, using a higher threshold for minimum sample size, we would have insufficient data for most lower-volume models, as well as new models introduced late in the model year. With smaller sample sizes, we would be more limited in our ability to detect differences among models, although we would then have sufficient data for more models.

The minimum sample size of 100 cars allows a good balance for us to provide accurate information on model differences, while still covering a majority of models on the market.

Why is there no reliability information for some models?

Consumer Reports sets a minimum sample size of about 100 cars; this size sample allows us to ensure that we have sound feedback from our subscribers to properly gauge the reliability of a model. We won't offer reliability information on those models for which we do not have a sufficient amount of data to draw a solid conclusion.

Our sample size generally tracks well with consumer market sales but may not correlate well with models that have high fleet sales. However, if a new model is introduced to the market at a time of year that does not coincide with our survey period, we might not get sufficient samples on that new model.

Are all automotive problems included?

Respondents to our survey are asked to identify problems they have experienced in a 12-month period in any of 17 trouble spots. We do not publish scores for advanced safety systems and air bags since the problem rates in the area are almost universally very low.

What do the trouble areas cover?

We have been revising the trouble areas since our 2007 survey to be more comprehensive and more closely reflect problems in newer vehicles and better define areas with high problem rates. The following are some changes:

Starting with the 2010 survey, Engine electrical now includes hybrid battery and related system in addition to other charging and ignition systems.

The trouble spot Transmission is separated into Transmission major (more serious problems such as transmission rebuild or replacement and torque converter) and Transmission minor.

Body Hardware includes power components which were formerly under Power equipment.

Our Reliability History charts cover problems in any of 17 trouble areas. Here's a look at what's covered in each of those areas:

ENGINE MAJOR: Engine rebuild or replacement, cylinder head, head gasket, turbocharger or supercharger, timing chain or belt.

ENGINE MINOR: Oil leaks, accessory belts and pulleys, engine mounts, engine knock or ping.

ENGINE COOLING: Radiator, cooling fan, water pump, thermostat, antifreeze leaks, overheating.

TRANSMISSION (AND CLUTCH)-MAJOR: Transmission rebuild or replacement, torque converter, clutch replacement.

TRANSMISSION (AND CLUTCH)-MINOR: Gear selector and linkage, transmission computer, transmission sensor or solenoid, clutch adjustment, rough shifting, slipping transmission.

DRIVE SYSTEM: Driveshaft or axle, CV joint, differential, transfer case, four-wheel-drive/all-wheel-drive components, driveline vibration, electrical failure, traction control, electronic stability control (ESC).

FUEL SYSTEM/EMISSIONS: Check-engine light, sensors (O2 or oxygen sensor), emission-control devices (includes EGR), engine computer, fuel-injection system, fuel cap, fuel gauge/sender, fuel pump, fuel leaks, stalling or hesitation.

ENGINE ELECTRICAL: Starter, alternator, hybrid battery and related system, regular battery, battery cables, engine harness, coil, ignition switch, electronic ignition, distributor or rotor failure, spark plugs and wires failure.

CLIMATE SYSTEM: A/C compressor, blower (fan) motor, condenser, evaporator, heater system, automatic climate system, electrical failure, refrigerant leakage.

SUSPENSION/STEERING: Shocks or struts, ball joints, tie rods, wheel bearings, alignment, steering linkage (includes rack and pinion), power steering (pumps and hoses, leaks), wheel balance, springs or torsion bars, bushings, electronic or air suspension.

BRAKES: Antilock system (ABS), parking brake, master cylinder, calipers, rotors, pulsation or vibration, squeaking, brake failure or wear.

EXHAUST: Exhaust manifold, muffler, catalytic converter, pipes, leaks.

PAINT/TRIM/RUST: Paint (fading, chalking, peeling or cracking), loose trim or moldings, rust.

BODY INTEGRITY: Squeaks, rattles, wind noises, loose or cracked seals, and/or weather stripping, air and water leaks.

BODY HARDWARE (Power or manual): Windows, locks and latches, doors or sliding doors, tailgate, trunk or hatch, mirrors, seat controls (movement and temperature), seat belts, sunroof, convertible top.

POWER EQUIPMENT AND ACCESSORIES: Cruise control, clock, warning lights, body control module, keyless entry, wiper motor or washer, tire pressure monitor, interior or exterior lights, horn, gauges, 12V power plug, alarm or security system, remote engine start.

AUDIO SYSTEM (excluding aftermarket systems): radio, speakers, antenna; CD or DVD player; GPS, iPod & MP3 interface; communication system (e.g. ONSTAR, Bluetooth), backup camera/sensors.

Are all problems considered equally serious?

Problems with the engine-major, cooling system, transmission-major, and driveline are more likely to take a car out of service and to be more expensive to repair than the other problem areas. Consequently, we weigh these areas more heavily in our calculations of Used Car Verdicts and Predicted Reliability. Problems in any area can be an expense and a bother, though, so we report them all in the Reliability History charts.

What different reliability scores does CR publish?

Consumer Reports uses the data from its Annual Questionnaire to compile detailed Reliability Histories on several hundred makes and models of cars, minivans, pickups, and sport-utility vehicles, spanning 10 model years. For each model that we have sufficient data, the Reliability History Chart shows you whether the model has had more or fewer problems than the average model of that year in each of 17 trouble spots. That information can be a big help when inspecting and purchasing a used car. The Used Car Verdict summarizes the 17 trouble spots for each model year and compares that to the average of all vehicles in the same model year. We use these Verdicts to identify lists of Reliable Used Cars and Used Cars to Avoid.

For new models that are currently available, our Predicted Reliability rating is based on the model's recent history, provided the model hasn't been significantly redesigned for the current model year. Online, Predicted Reliability is presented in the new car model overview pages in the Ratings Report Card, and Ratings & Specs and in the Vehicle Overall Ratings comparison. It is also incorporated into the Reliability History charts as the New Car Prediction.

We also present Predicted Reliability in more detail in our graphs. In this presentation, bar graphs show the percentage difference between each model's overall reliability and the average reliability of all models. We group models by vehicle type (for example, family cars or minivans), for ease of comparing models that are direct-market competitors.

Our statisticians also do in-depth analyses of the reliability data to provide information to consumers about trends in automotive reliability, reliability of newly introduced models, and other important issues. These analyses are presented in the April issue of Consumer Reports, at ConsumerReports.org, and in newsstand auto publications throughout the year.

What are the Reliability History charts?

The chart for an individual model will tell you where a model's strengths and weaknesses have been. Scores are based on the percentage of survey respondents who reported problems for that trouble spot, compared with the average model of that year. Models with problem rates close to the mean receive a

for that trouble spot. Models with scores of

or

are not necessarily unreliable, but they have a higher rate of problems than the average model. Similarly, models that score

are not necessarily problem-free, but they had relatively few problems compared with the average model.

In particular, within each trouble spot and within each model year, we create equal-width intervals for the

,

,

, and

, constructed so that the average model is the middle of the

, and the interval for the

begins at 0 percent.

An exception to this rule occurs when the mean problem rate is quite small (less than 2.5 percent), as is often the case in newer model years. In order to avoid making distinctions that are too fine to be meaningful, we do not assign a

unless the problem rate is at least 3 percent, or a

unless the problem rate is at least 4 percent.

How has this approach differed from the way it was done in previous years?

CR has changed the way it presents reliability data, beginning with the 2005 survey.

In previous surveys, the symbol for each trouble spot represented a specific range of problem rates. This allowed readers to make direct comparisons in the rate at which people reported problems in different trouble spots and in different ages of cars. However, this previous approach made it difficult for readers to make sense of whether a particular trouble spot was better or worse than average, and in some cases, it limited our ability to identify unusually reliable or unreliable cars. Also, the Used Car Verdict and Predicted Reliability are relative values that compare a vehicle's reliability record to the average model of the same age. The absolute scale of the trouble spots and the relative scale of the Verdict caused some confusion and frequent questions. So we changed our analysis in order to represent the data in a way that would be more clear and useful to readers.

In our new approach, scores are assigned separately within each trouble spot for models of each model year. For each trouble spot, we calculate the mean problem rate of all models of the same age, and then assign scores to an individual model based on how that model compares with the mean. In this new approach, a

or a

always represents a model with more problems than the average model of that age; and a

represents a model with fewer problems than average. (There is an exception in the newer model years, in which most trouble spots have very low problem rates. In those cases, even the average problem rate is excellent, and

represents that average.)

What is the Used Car Verdict?

The Used Car Verdict summarizes a model's reliability over all 17 trouble spots. Because problems with the engine major, cooling, transmission-major, and drive system can be serious and more expensive to repair, our calculation gives extra weight to problems in these areas. The Verdict scores show whether the model had more or fewer problems overall than the average model of that year.

What is Predicted Reliability?

The Predicted Reliability, also called New Car Prediction, forecasts how well a new model that is currently on sale is likely to hold up based on its recent history. For this Rating, we average a model's Used Car Verdict for the newest three years, provided the vehicle did not change significantly in that time and hasn't been redesigned for the upcoming model year. Over the years, we have found that several years of data are a better predictor than the most recent model year alone. One or two years of data may be used if the model was redesigned within that three-year time frame, or if there were insufficient data for some years.

Sometimes, we will make a prediction for a newly redesigned model if the previous generation has a track record of consistently outstanding (above average) reliability. Of course, this is only a prediction, and these scores are not a guarantee of the reliability of any individual car. However, buying a car that has an above-average score for Predicted Reliability will reduce the likelihood of having significant problems with your car.

You can find our Predicted Reliability for new cars in many of Consumer Reports' auto publications, including the April Annual Auto Issue, CR monthly road tests, our special new-car publications such as Best & Worst New Cars, New Car Buying Guide, on-line in ConsumerReports.org, and our New Car Price Reports.

How do you decide on Reliable Used Cars and Used Cars to Avoid?

Each year, we list the best and worst used cars from the current survey, usually a few months after the new cars have been updated. Reliable Used Cars are specific models with above average overall reliability, based on the Used Car Verdict for that model. To help you choose a reliable used car that meets your budget, we list Reliable Used Cars in price categories, from less than $10,000 to $25,000 and up. Within each car type and price range, models are listed alphabetically by make, model and year. We also compile a Best of the best list, CR Good Bets, which are models that have had consistently better-than-average reliability for multiple years, and performed well in CR's tests when they were new. Note that just because a model is not listed as a Reliable Used Car or a CR Good Bet does not mean that it is necessarily unreliable—it may be the case that we do not have sufficient data to assess its reliability, or that we do not have a recent enough road test.

Why are there sometimes considerable differences in reliability between "related" or "twin" models?

Some variants of similar vehicles have different reliability results in our survey. Although you might expect that related vehicles, or "twin" models, would have very similar reliability histories, there are a number of factors that can lead owners to have different reliability experiences with these models.

Some differences can be attributed to different equipment, such as different suspension tuning, or power equipment.

Some related models may be manufactured in different plants. While their designs might be quite similar, by being built in separate facilities they may be subject to different manufacturing processes, such as differences in quality control.

Some related models that share the same powertrain but have other differences such as model introduction at different times, may have different reliability. Models that are introduced later may benefit from solving of initial problems of the related model that was introduced earlier.

We carefully examine the data for all related models, and if the data show that their reliability profiles are similar, we will combine their data to yield more robust results. We believe, though, in the accuracy of our data, and we have a commitment to report the experiences our subscribers share with us. In some cases, they report different reliability experiences with closely related models.

Buying a reliable new car

New car buyers can get an idea of how a model that is currently on sale is likely to hold up by looking at the New Car Prediction. For this Rating, we averaged a model's Used Car Verdict for the newest three model years, provided the vehicle did not change significantly in that time and has not been redesigned for the new model year. We have found that three years of data are a better predictor than the most recent model year alone. One or two years of data may be used if the model was redesigned in recently, or if there were insufficient data for some years. Sometimes we include a prediction for a model that has been newly redesigned, provided its reliability history has been consistently above average.

While reliability history is no guarantee of a new car's reliability, by choosing a car that has been relatively problem-free for owners of recent models, you can improve your odds of having a problem-free car.

Buying a reliable used car

If you want to check on the reliability of a particular used car, start with the Used Car Verdict. This score shows whether the model had more or fewer problems overall than the average model of that year, calculated from the total number of problems reported by subscribers in all 17 trouble spots. Because problems with the engine-major, transmission-major, engine cooling, and drive system can be serious and expensive to repair, our calculations give extra weight to problems in those areas.

If you aren't sure which models to consider, start with our listing of the Best of the best. These are models that have consistently scored above average in reliability and performed well in our tests when new. The list of Reliable Used Cars can direct you to models that have been more reliable than the average models of their age, and that meet your budget. The Used Cars to Avoid list will tell you which models have more problems than the average car of the same age.

For any individual model you are considering, look at its Reliability History chart to see which of the 17 trouble spots may point to potential problem areas. These scores give an indication of whether other owners have had more or fewer problems than the average model of that age, but cannot tell you anything specific about the individual car you are looking at. Be sure to check those components particularly carefully before you buy.

What can I expect if I buy a car based on CR's reliability recommendations?

In general, cars have more problems as they age. A model that has proven reliability is likely to have fewer problems than other models, even as it ages. But even models with better than average reliability were not necessarily problem free, particularly in older models. In some of our most reliable 10-year-old models, about 70 percent of owners reported a problem-free year—of course that means that 30 percent of owners experienced some kind of problem. But models that receive better-than-average reliability scores had fewer problems than the average model of the same age.

How does a model's reliability affect whether or not it is recommended by CR?

Reliability is an important factor in our decision whether or not to recommend a model. In order to earn a CR Recommendation, a model needs to meet three criteria:

• The model needs to do well in our road tests.

• The model must have at least average Predicted Reliability.

• If the model was crash-tested by the National Highway Traffic Safety Administration (NHTSA) or the Insurance Institute for Highway Safety (IIHS), it must perform at least adequately. In addition, pickups and SUVs must not have tipped up in the government's rollover test.

A model that does not earn a Recommendation is not necessarily one we suggest you avoid. It might fall short of earning a recommendation because we haven't tested it recently, or because we do not have sufficient data to predict reliability.

If CR tested a model, it might not be recommended because it did not score well in our road tests or IIHS and NHTSA safety tests, or because it had below-average predicted reliability. In those cases, there are often better choices of vehicles for you to consider. Refer to our Vehicle Ratings comparison for vehicles that scored well overall and are recommended.

How can a car be recommended one year but not the next?

Our subscribers tell us about their experiences each year. In each Annual Questionnaire, we ask subscribers to ConsumerReports.org and Consumer Reports magazine about problems that they had experienced in the preceding 12 months. As their reports change from one year to the next, our Predicted Reliability scores sometimes change as well.

Some cars develop more problems as they age. As manufacturers make both major redesigns and minor changes to their models, the reliability of those models may change. We have seen that when a model is redesigned, it often experiences more problems in its first year following the redesign. Often, the reliability picture improves for those models in subsequent years, as the manufacturer works out the design and manufacturing "bugs." In fact, the last year before a major redesign might have the best reliability of a model's life cycle.

In some cases, a model is sufficiently redesigned that we cannot use our road test results or our Predicted Reliability data from the previous generation of that model to decide on a recommendation. Once we have the opportunity to road-test the new model and to collect sufficient reliability data, it may earn a Recommendation once again.

Is this a scientific survey?

There are generally two criteria that social scientists use to evaluate the quality of a survey: its validity and its reliability. Validity refers to whether the survey actually measures what it says it does. Reliability refers to whether the information generated by the survey would be repeated if the survey were to be conducted again.

We have strong evidence that our survey is both valid and reliable. The questions in the survey are designed professionally by experts in CR's National Research Center, in consultation with our automotive engineers and statisticians. Members of our survey team have more than 30 years of experience in conducting all sorts of consumer surveys. The survey uses an aided response technique that leads respondents through well-defined specific items and gives each respondent the same perspective in answering the questions. The data we report tracks well with other sources of repair and reliability information available on the market. Although we know that auto manufacturers pay close attention to our reports, they have not formally disputed our survey findings, which often identify problems that the manufacturers see in the warranty experience of their vehicles. We conduct a validation test every year and, in more than 30 years, have not found any evidence of bias. From year to year, our subscribers' reports of their problem experiences are fairly consistent; when there is a difference on a particular model, we can often attribute it to known issues with a particular component of a car.

Is the survey based on a representative sample?

A sample is considered to be representative of a population if the relevant characteristics of the population are reflected in the sample. So, considering the population of interest is critical in evaluating the quality of a sample. Our survey sample is drawn from the population of subscribers to ConsumerReports.org and to Consumer Reports magazine. While all subscribers are invited to participate in the survey, participation is voluntary, and there is always the possibility that those who respond are unique in some particular way. For example, subscribers have sometimes questioned whether those who respond are those who have a complaint to make about their cars.

To address this concern, we conduct a validation test every year. A representative sample of 8,000 to 10,000 subscribers are mailed the same questions about problem experiences with their cars at the same time as all subscribers are asked to complete the main survey. Using a combination of incentives and follow-up mailings, we attain at least a 40 to 50 percent response rate on this validation sample. The validation sample is known to be representative of the subscriber population; by comparing responses from this sample to responses of the main sample, we can assess whether the main sample is representative of the population overall. In more than 30 years we have not found any biases on any of the questions on any of the topics.

One reason for this is that our survey is an omnibus survey asking subscribers not only about their cars, but about a dozen other products, about major services they have used (such as insurance, hotels, and health plans), as well as suggestions for CR. The survey also requests participation in our board of directors election. Many subscribers return surveys reporting that they had no problems at all with their cars in the past year. This is true for all makes and models of cars. So, owners with complaints about their cars are not the only ones who return the survey.

Any survey has some sort of sampling frame that limits the people being surveyed. We choose our subscribers as our sampling frame. On average, CR subscribers tend to be more educated and affluent than the general population. With the growth of Consumer Reports online, a wider demographic range of individuals has been surveyed in recent years. However, our reliability questions do not ask respondents about their attitudes or opinions about the reliability of their cars, where one might expect different groups of individuals to have different perspectives. Instead, we ask for factual information about whether specifically defined problems occurred; these types of questions are less sensitive to the nature of the characteristics of the sample itself.

Further, our results track well with other sources of reliability information available on the market, and auto manufacturers have not formally disputed our survey findings, which often correspond to problems that the manufacturers see in the warranty experiences of the population of car owners at large.

Is the survey biased toward Japanese cars?

In our survey of CR subscribers, Japanese vehicles are popular. Also, many Japanese models have had relatively low rates of problems in our survey. But the fact that we received responses on more than 300 makes and models from nearly all domestic, European, and Korean manufacturers shows that our subscribers do not exclusively favor Japanese vehicles and that they buy a wide range of vehicles of all makes and models.

Unlike some other magazines or surveys, we do not take advertisements from any outside manufacturer, so we have no vested interests in the outcome of our survey. We have no agenda other than communicate accurate results of our survey. We do not consider country of origin in our analyses leading to our reliability ratings.

Some Japanese models in our survey have scored below average in reliability, and some American models for example, the Buick Verano and Chevrolet Tahoe have scored above average. Those findings provide evidence against pro-Japanese bias on the part of our subscribers.

European luxury brands' have made recent progress in CR's latest survey. The 4-cylinder version of both the Audi A6 and BMW X1 led the best predicted reliability score in both the luxury car and compact luxury SUV segments respectively, besting the Japanese models.

Your survey results do not match with my experience. Is your survey wrong?

The CR reliability information reflects the problem rate, or percentage of cars that experienced problems, across at least 100 car owners. Even in the most unreliable models, some individual car owners are lucky and experience few or no problems during the 12 months covered by the survey. For example, in one of the worst models in our recent surveys, about 75 percent of the owners reported problems in at least one trouble area over the previous 12 months; of course, this means that about 25 percent of owners reported no problems. Your neighbor or friend might be one of those lucky owners. Of course, the opposite can happen as well—even in a model that tends to be quite reliable, there is an occasional "lemon."

Since the average number of problems is small for most models, is Consumer Reports overemphasizing differences that may not be important?

Beyond statistical significance, we believe these differences are also meaningful to car buyers. We think that car buyers should expect a new car to be entirely problem-free in its first months or years of service. While the difference between a

and a

may be small, a pattern of several less-than-perfect trouble spots in a brand new car should be cause for concern and does not bode well for a model's long-term reliability. We have not yet seen a single model in our survey that is entirely problem-free. More than that, the Ford C-MAX Energy (Plug-in Hybrid), which had the worst new car prediction score in the 2013 survey, is about 11 times more likely to have a problem than the best, the Subaru Forester (non-turbo). Those differences among models are important for car buyers to consider in choosing a car. We present these scores for trouble spots primarily to allow consumers to compare the relative incidence of problems among models. While there are no guarantees, you can improve your odds of buying a reliable car if you choose a model that has had a lower rate of problems in the past.

Some people maintain their cars differently from others. How does this affect the Ratings?

Areas of concern in late-model cars include the body integrity (squeaks, rattles, and leaks), body hardware (locks, seats, and doors), and audio, entertainment, communication, and navigation system. Maintenance does not affect those items. Problems in those areas might more likely reflect the inherent design or quality.

How do you account for mileage differences?

Vehicles with higher mileage will most likely experience more problems than vehicles of the same age with lower mileage. We adjust our analyses to minimize differences among models due to varying mileage. Our data are mileage-standardized by dividing cars of each model into groups of high, average, and low mileage, and employing the statistical technique of direct standardization.

How do you know that manufacturers don't "stuff the ballot box?"

In most other surveys that draw their samples from lists of registered car owners, the researcher can control who is mailed a survey. In the Consumer Reports survey, buying a subscription to either the magazine or to ConsumerReports.org allows you to report on your experience with two cars. Some subscribers have wondered whether a manufacturer could just arrange to have their employees fill out questionnaires saying that their cars are reliable, as a way to influence our Ratings. Hypothetically, this is a potential weakness in our survey.

However, there are a number of ways that we can protect against this potential for fraud. For obvious reasons, we do not want to describe in detail the actions we take in this regard. We are confident that no manufacturer has succeeded.

If you state that first-year models are less reliable than later-year models, how can you still recommend some new Japanese models in their first year?

It is true that some newly introduced or redesigned models have more problems than later model years of that design. This happens even to models from the most reliable manufacturers, such as Toyota/Lexus/Scion and Honda/Acura. But despite the decline in reliability due to the new design, if the new/redesigned model still earned an average predicted reliability, and performed well in our testing and independent crash and rollover tests, we will recommend it. We will not recommend any model that has below average predicted reliability regardless of how well it performed in our testing. Occasionally, we will recommend a newly redesigned model with no reliability data specific to that design if the previous generation has a consistently outstanding reliability track record based on our surveys.

Are cars getting more reliable than they used to be?

Yes. In the past 20 years, the reliability of all vehicles has improved greatly, on average. Of course, some models have remained quite unreliable, while others have improved quite dramatically. American models have made the greatest improvements, but they historically have had the most improving to do. Asian models have improved as well, so the gap between domestic and foreign cars has narrowed, but it still remains.

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