ACARA v9 CONTENT DESCRIPTION “compare methods and findings with those of others, recognise possible sources of error, pose questions for further investigation and select evidence to draw reasoned conclusions”
Builds on running a fair test and reading a graph. Two groups set out to measure how the shadow of the same pole changes through the day. They followed slightly different methods and ended up with somewhat different findings. The job now is to compare those methods and findings, recognise a likely source of error, select the evidence that holds up, and pose a sharper question to investigate next.
Compare methods, not just findings
When two groups investigate the same thing and get different answers, the first move is to line up what each group actually did. Group A measured the pole's shadow in the morning; Group B measured it in the early afternoon. Both wrote careful numbers, yet the numbers do not match. That gap is a clue, not a contest. Comparing the methods often explains the gap and tells you which findings you can trust.
Two groups' shadow lengths side by side
Both groups measured the shadow of the same pole at five marked points and recorded its length in centimetres. Switch between the table, bars and line to compare their findings.
My group's lengths, measured across the morning. The other group measured 74, 49, 40, 55 and 90 cm. Both sets dip to their shortest in the middle and rise at the ends, so the groups agree on the pattern: the shadow is shortest when the Sun is highest. Findings that share a pattern across groups can be trusted more, even when the exact numbers differ.
Recognise a possible source of error
Before trusting a comparison, look for a source of error: something that pushes a measurement away from the true value. Here the two groups measured at different times of day, so the Sun sat at different heights and cast different shadows. Other sources of error could be a ruler held on a slant instead of square to the ground, or measuring on an uneven patch of paving. When findings disagree, an unrecognised source of error is often the reason, so it is the first thing to hunt for.
Find the reading with a source of error
Five students each measured the same shadow at the same mark, at the same time. Four readings sit close together, but one is far off. Click the reading that does not match the others.
Click the point that does not fit the pattern of the others.
Weigh the method differences
Not every difference between the two methods matters the same amount. Some differences are the real source of error behind the mismatched findings; others barely change the result. Weigh each method difference to decide which one most likely caused the gap. The one that changes the conditions of the measurement is the one to fix in the next test.
Which method difference most likely caused the gap?
The two groups did three things differently. Pick each one to see what it gains in convenience and what it costs in fairness, then decide which is the real source of error.
Group A and Group B both measured the same pole's shadow, but their methods differed in three ways. Choosing each difference shows what it gives and what it gives up when you try to compare the findings fairly.
Choose a response to see what is gained and what is given up.
Select evidence for a reasoned conclusion
A reasoned conclusion rests only on the evidence that holds up. The readings taken at different times of day cannot be compared fairly, so that evidence is set aside. What remains is what both groups measured the same way: the shadow was shortest near the middle of the day and longer when the Sun was low. Sort which statements the surviving evidence supports, and which should be left out.
Which evidence supports the reasoned conclusion?
The conclusion should rest only on evidence both groups can stand behind. Decide which statements the shadow measurements actually support.
Claim: A pole's shadow is shortest near the middle of the day and grows longer as the Sun gets lower.
Both groups found the shadow at its shortest near the middle of the day.
Both groups found longer shadows at the start and end, when the Sun was low.
In both groups, the graph dips in the middle and rises at the ends.
One group measured in the afternoon and the other in the morning, so those readings cannot be compared fairly.
Our group used a bright yellow ruler, which we liked best.
Decide whether each statement is evidence for the claim, or not.
Why this matters
Comparing methods as well as findings, recognising where error creeps in, selecting the evidence that holds up, and posing a sharper question are the steps that turn two messy sets of numbers into a conclusion you can trust. Scientists do exactly this when results from different labs disagree: they compare methods, find the source of error, and design a cleaner test.
Quick self-check
1. Two groups measured the shadow of the same pole at hourly marks and got somewhat different lengths. Why is it worth comparing both their methods and their findings, not just the findings?
2. Group A measured at 9 am, 10 am and 11 am; Group B measured at 1 pm, 2 pm and 3 pm. The shadow lengths differ. What is the most likely source of error in comparing them?
3. A source of error is best described as something that...
4. After comparing the two groups, which is a good question for further investigation?
5. You are selecting evidence to draw a reasoned conclusion about how shadow length changes. Which piece should you set aside?