SHSAT: Informational reading: how models are tested and revised
Learn the path that passages about models usually follow (purpose, simplification, test, mismatch, revision, limits) and use it to answer central-idea and purpose questions.
When a passage describes people building and testing a model, how do you keep track of what each part is doing?
Short answer
Track what the model keeps, what it leaves out, how it is checked against reality and what changes after a mismatch. Then test each answer against every one of those stages.
Know first: Cause and effect, Central idea
Step 1 of 5
Models simplify on purpose
A model is a simpler version of something real: a cardboard city, a computer map, a sandbox river. It keeps the features that matter for one question and leaves out the rest.
Passages about models tend to follow a path. People build a model for a question, test its predictions against the real thing, find a mismatch, revise the model, and admit what it still can't show. Questions ask about each stage.
| Stage | Ask |
|---|---|
| Purpose | What question is the model built to answer? |
| What is kept | Which features matter for that question? |
| Test | How do people check the model against reality? |
| Mismatch | What didn't match, and what caused it? |
| Revision and limits | What was fixed, and what can the model still not show? |
Step 2 of 5
Follow one model from test to revision
An excerpt
[1] A math class built a tabletop model of the cafeteria line to predict where students would crowd together at lunch1. [2] They used one token for each student and moved every token forward one square per count2, since most students walk at about the same pace. [3] At lunch the next day, the crowd formed at the milk cooler, not at the register3 where the model had predicted. [4] Students who stopped to choose a carton held up everyone behind them, and the model had let every token move at the same speed4. [5] The class added a two-count pause at the cooler, and the revised model put the crowd at the cooler too. [6] They noted that tokens could not show students who stepped out of line to talk with friends5.
- Purpose.
- What is kept, simplified: everyone moves at one steady pace.
- Mismatch.
- Cause: a simplifying assumption inside the model.
- A limit that remains.
Worked example: What does the milk cooler show?
What does the milk cooler episode in sentences 3 to 5 most clearly suggest?
- AThe class should stop using models and simply watch the line every day.
- BA simplifying assumption can hide the cause of the very problem a model is built to predict.
- CThe milk cooler causes every delay in the cafeteria.
- DThe class counted the number of students incorrectly.
- 1
Find the mismatch
The crowd formed at the cooler, where the model predicted none.
- 2
Find the cause
The model let every token move at the same speed, but students stop at the cooler. The simplification left out the pause.
- 3
See what changed
They added a pause at the cooler, and the revised model put the crowd in the right place.
- 4
See why the others are there
A treats one mismatch as a reason to give up. C stretches one stop into the cause of every delay. D blames the count, but the passage names the equal-speed assumption.
Answer
B. A simplifying assumption can hide the cause of the very problem a model is built to predict.
Wrong: The cafeteria model was wrong, so the class stopped using it.
Right: The cafeteria model was wrong at the cooler, and the class revised it.
The second statement fits sentences 5 and 6, which show the class changing the model and naming a limit. Check what people do after a mismatch.
Step 3 of 5
Ask what each part of the passage is for
Check yourself · Question 1
Why did the class move every token forward at the same pace?
Answer: B
Sentence 2 gives the reason: most students walk at about the same pace. Moving every token one square per count keeps that feature simple.
Check yourself · Question 2
Why does the author include sentence 6?
Answer: D
After the revision works, sentence 6 names something the tokens still can't show. It is an honest limit.
Trap answer: To show that the class gave up on the model.
Treating a limit as failure
- Why it looks right
- Sentence 6 admits a weakness, and admitting a weakness can sound like giving up.
- Why it's wrong
- The class names the limit after improving the model. Naming a limit is part of using a model well.
- The right answer
- Sentence 6 admits a behavior the revised model still can't represent.
Common mistake
Since the model missed something, I picked the answer saying models aren't useful.
- Why it's tempting
- A mismatch looks like proof that the model failed.
- Do this instead
- Read what the people in the passage do next, and let every stage, not the mismatch alone, decide your answer.
Step 4 of 5
What to remember
Remember
- Track a model's purpose, what it keeps, how it is tested and how it changes.
- A mismatch points to something the model left out or simplified; find it before you judge the model.
- Test each answer against every stage of the passage, including what happened after the mismatch.
Step 5 of 5
Practice on a real question
Use what you just learned on this question, then check the explanation.
In your own words
In the practice passage, what did the students' model get wrong at first, and what did they do about it?