Separate source expertise from agreement with its conclusion

To judge a source fairly, ask two separate questions: does this source have good reason to know about this topic? and do I agree with where it ends up? Keep the answers apart, because mixing them is the quickest way to misjudge evidence.

This skill is used whenever you evaluate a source in Global Perspectives, and it builds directly on tracing a claim to its original source. It belongs to sources and credibility. The people and organisations below are invented for practice.

What makes a source knowledgeable about a topic?

Four checks cover most cases. None needs you to know the answer in advance.

• Relevant expertise: training or experience in this exact topic, not a nearby one.
• Access to evidence: did they collect data, observe directly or read the original material?
• Method: can you see how they reached their conclusion?
• Interest: would they gain or lose depending on the outcome?

Each check is a clue, not a verdict. Together they help you decide how much weight to give the source and what to check next.

How to separate expertise from agreement, step by step

1. State the question the source is answering in one line.
2. Write the source’s conclusion, then set it aside. Do not rate it yet.
3. Run the four checks on the source itself.
4. Rate the source’s reliability for this question (for example: strong, partial, weak) and give one reason.
5. Only then compare the conclusion with your own view and with other sources.

Worked example (invented sources)

Question: Should Millbrook Council extend the bus network to the north district?

Source 1: Dr Mira Alden, a soil scientist, says the extension is a bad idea because it will “obviously cost too much”.

Source 2: Ben Okoro, a transport planner who worked on the council’s last route review, says the extension is a good idea and publishes his passenger counts and method.

Step 1, question: about cost and benefit of a bus route.

Step 2, conclusions: Alden says no. Okoro says yes. You happen to prefer “no”.

Step 3, checks. Alden: expertise is soil science, not transport costs; no data given; no method shown; no interest declared. Okoro: expertise is directly relevant; he gives data and method; he may favour projects he worked on, which is a possible interest.

Step 4, rating. Alden is weak for this question. Okoro is stronger, with a note to look for independent passenger figures.

Step 5, compare. Your own preference for “no” does not change the ratings. Your next move is to look for other sources that test Okoro’s counts, for example the council’s published budget.

The mistake to watch for

A common slip is to rate sources by whether they agree with you.

Mistaken approach: “Okoro must be biased because he wants the extension, and Dr Alden is a doctor so she must be right.”

This treats a title as proof and an interest as a verdict, and it gives the better-matched source less weight because of the conclusion.

The correction is to rate each source on the four checks first, and write one reason for each rating. Disagreement with a conclusion is a reason to look for counter-evidence, not a reason to lower the source’s rating.

Check yourself

1. A famous footballer says a new diet removes fatigue. What do you check before giving the claim much weight?

2. A source with strong expertise reaches a conclusion you dislike. What are two sensible responses?

3. A water company reports that its own tap water is “the healthiest in the region”. Which check is most relevant here?

Where this leads next

With the source judged, look closely at what it claims. The next skill is checking the date and context of a numerical claim. When you are ready, use the sources and credibility practice set.

Students often know the checklist but apply it differently to sources they like. In online one-to-one Global Perspectives tuition, a teacher can supply fresh, non-assessed examples so that you practise the habit rather than the answer.