Lab Analysis
Overview
Learn to analyze experimental data, identify sources of error, and draw valid conclusions from laboratory results.
Practice Problems
Question 1: Data shows plant heights of 12, 13, 11, 12, and 47 cm in the control group. What should you do with the 47 cm value?
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Answer: Investigate as a potential outlier - check for measurement or recording errors
Don't automatically remove outliers. Determine if it's an error (remove) or unusual but real data (keep and note).
Question 2: An experiment tested 3 fertilizers. Group A: 15, 18, 17 cm. Group B: 22, 25, 23 cm. Group C: 16, 15, 17 cm. Which fertilizer appears most effective?
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Answer: Group B (average ~23 cm vs. ~17 cm and ~16 cm for others)
Compare averages, but also note consistency. Group B has both higher average and consistent results.
Question 3: What's the difference between accuracy and precision?
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Answer: Accuracy = how close to the true value; Precision = how consistent/reproducible the measurements are
You can be precise but inaccurate (consistently wrong) or accurate but imprecise (right on average but scattered).
Question 4: Results show treatment group improved 5% more than control. Is this significant? What would help determine this?
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Answer: Need sample size, variability, and statistical tests to determine significance
5% could be meaningful or just random variation. Statistical analysis determines if differences are likely real.
Question 5: A student's hypothesis predicted the opposite of what happened. How should they write the conclusion?
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Answer: State that data did not support the hypothesis, explain what actually happened, suggest revised hypothesis
Be honest about results. Unsupported hypotheses are not failures - they're valuable findings.
Question 6: Identify a source of error: Students measured water temperature, but the thermometer touched the beaker bottom.
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Answer: Systematic error - the beaker may be warmer/cooler than water, giving consistently incorrect readings
This error affects all measurements the same way. Solution: Keep thermometer suspended in water, not touching glass.
Question 7: A graph shows time on x-axis and distance on y-axis. What does the slope represent?
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Answer: Speed (rate of change of distance over time)
Slope = rise/run = change in y / change in x = distance/time = speed.
Question 8: Why should you include error bars or ranges when reporting data?
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Answer: They show variability and uncertainty in measurements, helping readers judge reliability
A reported average of "25 cm" is incomplete without knowing if individual values ranged from 24-26 or from 15-35.
Question 9: Two variables show correlation. Can you conclude one causes the other?
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Answer: No - correlation does not prove causation
A third variable might cause both, or the relationship might be coincidental. Controlled experiments are needed for causation claims.
Question 10: What belongs in a complete lab conclusion?
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Answer: Restate hypothesis, summarize key results, explain whether hypothesis was supported, identify errors/limitations, suggest future research
A conclusion interprets data - it doesn't just repeat it. Connect findings back to the original question.