Ultimately what distinguishes one person holding an opinion from another is what they know about the subject and what that knowledge is based on, that is, facts or just opinions. Their accuracy and effectiveness in the past, together with their level of expertise, is what built their credibility. Their credibility is what enables you to judge how much you can trust them to be knowledgeable on the subject in question.

When you are faced with multiple opinions you must evaluate the credibility of your sources. Once you know how credible each is you can ascertain whose opinion is the most reliable and you will know whom to trust.

How can you determine credibility?

There are several factors you must take into account to determine how credible a source may be:

• Your previous experience with that source: Have you dealt with them before? Do you have any reason to doubt them?
• The source’s potential bias: Does the source have any vested interest in expressing one opinion over another?
• The source’s level of expertise: What are the source’s credentials? What makes them qualified to express an opinion on the subject?

Let’s go through an example of an analysis we can make when we are presented with an argument so we can ascertain its validity. Take a look at the old Coca-Cola™ ad below: 

There are several claims being made there:

1. It’s delicious
2. Relieves fatigue
3. The most refreshing drink in the world
4. Better than ginger ale, seltzer or soda

The first claim, that it’s delicious, is totally subjective and thus cannot be questioned or disputed. The second claim, that it relieves fatigue is a questionable one. How do we know? Has there been any clinical studies made in which some tired people drank Coca-Cola and some others drank generic colored sweet soda water and then they somehow measured whether the ones that drank Coke were less tired? And if so, who were the subjects? And who conducted the study?

How about the third claim? In reality there are multiple sub-claims here: that the drink is the most refreshing, that it’s refreshing, and that those things are true of the entire world.  

Again, how did they determine this? Did Coca Cola take a world-wide survey of people who drank Coca-Cola, and also drank every other drink in existence to be able to conclude Coca-Cola was the most refreshing in the world?

Same thing applies to the fourth claim: better according to whom? And better in what way?

So, in order to assess how credible a source might be you must evaluate whether they might be biased and you must know their level of expertise on the subject matter at hand. If you dealt with that source before and it proved to be untrustworthy then you can discard it or at least be very skeptical about it. It’s critical you know who makes the claim. 

Lets take a deeper look at bias and level of expertise.

How to recognize bias

Biases are very common tendencies people have that make them favor one side of an argument over another, or make them susceptive to hold a prejudice against other sides, or make them partial against something. Biases can manifest themselves in several ways:

• Expressed as direct statements.
• Indirectly in the words chosen to express something.
• In the tone of voice in which the person expresses himself.
• In the choice of facts or examples chosen to illustrate a point.

Biases are a reflection of our opinions and of our views on life.

It’s perfectly normal and very common for someone’s views to be colored by his biases. Therefore, it is very important that you use your critical thinking skills to recognize the bias filter your interlocutor is using. This will enable you to remove the layers of prejudice and extract the neutral truth from what he is saying.

Conversely, it is important you recognize your own biases and make an effort to try to be as neutral and as free of prejudice in what you say as possible.

All this takes practice and a conscious effort, but it will pay off in the long run as you are able to build a reflexive bias detector that will get you closer to the truth.

In practical terms, you should look for one or more of the following clues to help you detect bias in what you read or hear. If you identify any of this when discussing a subject then you are likely witnessing the use of bias:

• Excessively positive or negative expressions about the subject.
• Emotionally charged language used to describe the issue.
• Vague or generalized language used to refer to the subject.
• The omission of certain facts, particularly if those facts would go contrary to the position presented.
• The failure to present or cite the sources for the evidence presented.
• The knowledge that the person has something to gain by persuading us of his position.

Example

Let’s say you need to find a good auto mechanic to work on your new Ford Mustang. Since you are new to Mustangs you decide to do a little research to find a good, trustworthy mechanic.

• You check reviews online
• You ask you friend Joe who knows nothing about cars but is very happy with his mechanic, who works on all sorts of brands
• You also ask Jim who owns a Mustang himself and regularly takes it to the track
• You see an ad for an auto repair shop in your local newspaper

Everyone tells you what they think about their mechanics. The ad in the newspaper touts the shop as top notch. You end up with many opinions. How can you tell whom to trust the most?

In the auto mechanic example described in the sidebar above, the newspaper ad is highly likely to be biased as it surely used most of the points listed above to show the auto repair shop in the best possible light. Even if the repair shop was unreliable and untrustworthy you can be sure the ad will only mention any real or imagined good points about it and leave any negative points out. This is because advertising has a clear money-making purpose and thus you should always be very skeptical about it.

Imagine your neighbor holds loud parties every night and prevents you from sleeping. If he then recommends his car repair shop to you you may be less likely to believe what he has to say about it or you may even dismiss it altogether. In that case you would have disregarded the potential validity of his opinion because you let yourself be influenced by the annoyance of his nightly activities. This would be bad. You need to be able to separate how you feel about the neighbor from what he actually has to say.

Similarly, if your neighbor recommends a car repair shop and then you find out he has a stake in it or his brother owns it, then you can see that your neighbor would have something to gain by persuading you to use that repair shop. This does not necessarily mean that the repair shop is not as good as he claims, but knowing this about your source should give you pause when deciding how much weight you will give to his opinions.

Level of Expertise

The other important criteria you should use to determine a person’s credibility is that person’s level of expertise. Generally, the more a person knows about a subject, and the more rigorous that person was in acquiring that knowledge, the more reliable and trustworthy that person will be. That person will be more credible and thus you can feel safer in accepting their opinions. As a general rule, the greater the level of expertise, the greater the credibility.

To come back to the auto repair example we discussed earlier, we can now introduce the criteria of level of expertise in the analysis as that will allow you to further assess the credibility of each source.

In this particular case, expertise falls into two categories: knowledge of car repair, and knowledge of Ford Mustangs. Based on your source’s opinions about the repair shops they are recommending you can evaluate how much each of those repair shops might know about car repair in general and Ford Mustang repair in particular.

Let’s rank each of our sources based on their level of expertise in the two categories we identified. Use 1 for highest level of expertise and 4 for the least:

Knowledge of car repair:
      Online review
      Joe
      Jim
      Newspaper ad

Knowledge of Ford Mustang repair:
      Online review
      Joe
      Jim
      Newspaper ad

We can now combine what you learned about bias and level of expertise to help you asses each source’s credibility.

We identified several opinions we must consider:

• Online reviews
• Joe’s opinion
• Jim’s opinion
• The newspaper ad

You can quickly pare down the number of opinions by making a brief analysis of how credible each might be. Which one would you say is the least credible? You probably chose the newspaper ad, and rightly so. By definition, an ad is a biased source since they have a vested interest in portraying their product or services in the best possible light. You are not likely to see an ad that speaks negatively about that company or product! Besides, an ad does not tell us anything at all about actual level of expertise.

Which one is the next least credible source? If you chose the online reviews you would be correct. The reason why online reviews are untrustworthy is because they may be biased and also because you have no way of knowing what the level of expertise of each of those sources might be.

You can then consider what your friend Joe thinks. He

has a high opinion about his mechanic, but he admittedly knows nothing about cars.

So, you may arrive at the conclusion that Joe’s opinion is not so trustworthy because he really has no way to make a proper evaluation of his mechanic. Besides, his mechanic works on different brands, and even though he may be very

good he might not have a high level of expertise on your brand.

Lastly, you have Jim’s opinion. Jim is likely the most credible of the bunch because he knows a lot about cars generally (as someone who races), and about Mustangs in particular. People like Jim are likely to have tried many mechanics and if he really likes his that is a

pretty good hint that that mechanic is very good and knows Mustangs in and out.

This may have been an obvious example, but the purpose of going through this analysis is so you can understand the process of ascertaining whose opinion is the most reliable and thus know whom to trust. The same method can then be applied to any other situation.

Determining the Level of Expertise

There are some situations in which you must be more thorough in your evaluation of the source’s level of expertise. For example, when choosing a surgeon to operate on your daughter, or a pilot to take you to a remote island, or even an expert witness for a trial, you must use a more systematic and stringent approach to determine the credibility of the person in question, and their level of expertise plays a key role there.

In these situations we we must examine the following five criteria when assessing someone’s level of expertise, and therefore his credibility:

• Occupation
• Education
• Reputation
• Experience
• Achievements

These criteria are listed in no particular order and their relative importance may be different in each case.

I n conclusion, you must always consider the credibility of your sources when you are using them to help you make decisions or solve problems. You can evaluate the source’s trustworthiness by first removing the source’s potential for bias and then evaluating their level of expertise. You can judge the person’s level of expertise by assessing their education, experience, position, reputation and achievements. You will be able to tell whom to trust when the person scores high on all those points.