SHSAT: Inference: what a revised procedure is designed to show
Learn to infer the purpose of a second attempt by comparing what changed and what stayed the same, and to reject answers that promise results or inflate small details.
When a passage describes a first experiment and a revised one, how do you infer what the second one is for?
Short answer
Find the flaw in the first attempt, then list what the second attempt holds steady and what it lets change. Its purpose is to isolate that one changing factor; no design can guarantee a result.
Know first: What an inference is, Cause and effect
Step 1 of 5
The changes between two attempts reveal the purpose
An inference is a conclusion the passage supports without stating it. Passages about experiments often describe a first attempt, a problem someone notices, and a second attempt. The changes between the two attempts are your evidence.
The usual flaw is that the first attempt changed two things at once, so no one could tell which one caused the result. The second attempt fixes this by keeping everything the same except one factor. That one factor is what the new test is built to examine.
| The passage says | You can infer |
|---|---|
| Someone notes that two conditions changed together | The first result can't be traced to either one alone |
| The new trial uses the same materials, place, amounts or timing | Those factors are held steady on purpose |
| Only one condition is allowed to differ | The trial is built to isolate that condition |
| An accident is written down, not erased | The investigator is honest about a limit; the accident is not what is being tested |
Step 2 of 5
Let the comparison do the work
Two trials
Theo wanted to know whether wrapping a cooler in a towel kept ice frozen longer. In his first trial, he wrapped one cooler and left it in the shade, while an unwrapped cooler sat in the sun. His sister noted that the shade alone could explain the difference1. For the second trial, Theo placed two identical coolers side by side in the shade, each holding the same weight of ice2, and wrapped only one3. When a dog nudged one lid open for a minute, he recorded it in his log4.
- The flaw: towel and shade changed together.
- Held steady: cooler type, location, amount of ice.
- The one factor allowed to differ.
- An honest note about a limit. It is not the factor being tested.
Worked example: What can be inferred about the second trial?
What can be inferred about Theo's second trial?
- AIt proves that towels keep ice frozen longer.
- BIt measures how much shade and sunlight each matter.
- CIt lets Theo judge the towel's effect apart from other conditions.
- DIt makes the open lid the main factor Theo is studying.
- 1
Find the flaw
In trial one, the towel and the shade changed together, so the result could come from either.
- 2
List what stays the same
Cooler type, a shady spot and the weight of ice.
- 3
Name what changes
Only the towel. The trial is built to test the towel by itself.
- 4
See why the others are there
A is a guarantee answer; the trial hasn't even produced a result yet. B can't be right: both coolers now sit in the shade, so the trial doesn't compare shade and sun at all. D promotes the recorded accident into the purpose.
Answer
C. The design isolates the towel.
Wrong: The second trial shows that the towel works.
Right: The second trial makes it possible to tell whether the towel works.
The passage describes a design, not an outcome. An inference about purpose stays on the design side.
Step 3 of 5
Separate the design from the result
Check yourself · Question 1
A baker thought her new oven baked bread faster. On the first test, she baked a small loaf in the new oven and a large loaf in the old one. Her assistant pointed out that the loaves were different sizes. What was the main weakness of the first test?
Answer: B
A smaller loaf bakes faster in any oven, so the result can't be pinned on the oven. Size and oven changed together.
Check yourself · Question 2
For a second test, the baker made two loaves of the same size from the same dough and baked one in each oven at the same temperature. Halfway through, she turned both loaves so each side faced the oven door for the same time. Why did the baker most likely keep the loaf size, dough and temperature the same?
Answer: C
Same size, same dough, same temperature: only the oven differs, so a difference in baking time points to the oven.
Trap answer: To make sure the new oven would win the test.
Design mistaken for result
- Why it looks right
- The test is careful and fair, so it feels like it should settle the question in the new oven's favor.
- Why it's wrong
- A fair test makes any result easier to interpret. It can't decide in advance which oven wins.
- The right answer
- The choice about tracing a difference to the oven describes what the design does, which is all the excerpt supports.
Common mistake
The choice mentioned the interruption from the passage, so I figured it mattered most.
- Why it's tempting
- Accidents are vivid, and choices that mention them use the passage's own words.
- Do this instead
- Ask what the investigator planned to vary. A recorded interruption limits how you read the result. It becomes the purpose only if the passage says someone chose to test it.
Step 4 of 5
What to remember
Remember
- The flaw in the first attempt tells you what the second attempt is trying to fix.
- What stays the same is evidence too: it shows which single factor the test isolates.
- Cross out answers that promise a result or turn a recorded accident into the purpose.
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 second experiment keep the same, and what one condition did it allow to differ?