AP® English Language and Composition review sheet from Aim for Five (aimforfive.com/lang/units/6/6-2)
Unit 6 · Topic 6.2
6.2 Judging whether a source is reliable
Every source gives you information, but some sources deserve more trust than others. Before you build a claim on a source, check who made it, what they know, where and when it was published, and how well it backs up what it says. Judging reliability helps you choose evidence and explain why readers should believe it.
Key terms
- credibility
- reliability
- expertise
- publication
- evidence
Credible and reliable
A credible source is one readers have good reason to trust, usually because the author has relevant expertise or the publisher checks its facts. A reliable source is one whose information holds up: it's accurate, current and supported by evidence. The two usually go together, but not always. A famous expert writing outside their field may sound credible but be unreliable on that topic.
Reliability isn't all-or-nothing. Most sources are trustworthy for some purposes and weak for others. A personal blog post is a poor source for national statistics but a fine source for showing how one person experienced an event.
Questions to ask about any source
On the synthesis essay, each source comes with a short introduction giving the author, title, publication and date. That introduction is your evidence about reliability, so read it as carefully as the source itself.
| Question | What to look for |
|---|---|
| Who wrote it? | Relevant training, job or experience with this topic |
| Where was it published? | A publisher with editors or reviewers, or a site with no checks |
| When was it published? | Recent enough for the topic; old data can mislead on fast-changing issues |
| Why was it written? | To inform, to persuade, to sell, or to defend the author's own organization |
| How does it support its claims? | Data, named sources and methods, or only opinion and anecdote |
| Do other sources agree? | Claims that several independent sources confirm are stronger |
Using reliability in your writing
You don't have to avoid a weaker source, but you should use it for what it's good at. Use a government data table for numbers and a first-person account for how a policy feels to the people it affects.
When a source is especially strong, say why in a short phrase: "a ten-year study of 2,000 students," "a doctor who treats sports injuries." This tells the reader why the evidence matters, and it counts as commentary because it explains why the evidence supports your claim. When a source is weaker, you can still use it if you name the weakness and explain why the point survives (6.4).
Reliability on the multiple-choice section
Writing questions sometimes ask which added detail would make a passage more convincing or more credible. The right answer is usually the one with a specific, checkable basis, such as a named study or a precise number, that matches the claim exactly. A dramatic but vague choice is usually a trap.
Worked examples
Try each one yourself first, then open the solution.
- Example 1
Ranking three sources for one claim
Practice sources (written for this practice set; all invented): Source A: A 2025 article in a peer-reviewed education journal by two researchers who tracked test scores at 40 high schools before and after phone bans. Source B: A 2025 post on a phone company's blog arguing that phones help students learn. Source C: A 2016 newspaper column by a parent describing her son's distracted homework habits. Which source is most reliable for this claim: "Banning phones during class improves test scores"? Rank them and explain.
Show the solutionHide the solution
- Step 1: Match the source to the claim. The claim is about test scores across schools, so you need data from many schools.
- Step 2: Source A is written by researchers, reviewed by other experts before publication, recent, and measures exactly the outcome in the claim. It ranks first.
- Step 3: Source B is recent, but the company profits from phone use, so its purpose is to persuade. It may still show the opposing position, but it's weak support for any claim about scores.
- Step 4: Source C is one family's experience from years before phone bans became common. It can show what distraction looks like at home, but it says nothing about test scores.
Answer: A, then C, then B for this claim. A is recent, expert, peer-reviewed and measures scores directly. C is honest but anecdotal and off-target. B has a financial motive and doesn't measure the outcome.
Common mistakes
- Treating any source with numbers as reliable. Ask where the numbers came from and whether they measure what the claim is about.
- Rejecting a biased source completely. A source with an obvious interest can still show what one group thinks, which is useful evidence about perspective (6.3).
- Skipping the source introductions on the synthesis essay. The author, publication and date are what let you judge reliability, and they give you material for commentary.
- Confusing "credible" with "agrees with me." A source that supports your thesis isn't automatically trustworthy.
On the exam
- A short phrase explaining why a source deserves trust ("according to a federal survey of 30,000 households") makes your evidence stronger and shows the reader you've thought about it.
- In writing questions, prefer the answer choice whose evidence is specific, relevant to the exact claim and credible for the intended audience.
Connected topics
Videos
Check yourself
4 questions on 6.2 Judging whether a source is reliable. Pick an answer to see if you got it, and why.
Written for this practice set: four sources a student is reading before writing a synthesis essay on whether the city of Maple Falls should ban gas-powered leaf blowers. Maple Falls is fictional.
Which source is the least reliable as evidence about how loud gas blowers are?
Which additional information would most increase the reliability of Source A?
Written for this practice set: a student's draft of a synthesis essay, which cites sources by letter. The sources are invented.
The writer wants to replace Source B with a more reliable source about how the schedule affects families. Which source would be most reliable?
| Hours of sleep on school nights | Number of students (out of 40) | Average self-rated focus in class (1 = low, 5 = high) |
|---|---|---|
| Fewer than 6 | 9 | 2.1 |
| 6 to 7 | 17 | 3.0 |
| 7 to 8 | 10 | 3.6 |
| More than 8 | 4 | 3.9 |
Survey of 40 students at one high school, who answered both questions about themselves. Data invented for this practice set.
Which change to the survey would most improve its reliability as evidence about high school students in general?
0 of 4 answered