Confound — Science definition

A second factor that varied alongside the independent variable, so a difference cannot be attributed to either one.

Where it is taught

In use

And it protects you against a confound — a second factor that changed alongside the one you meant to test, so that when a difference appears you cannot tell which factor produced it.

Questions, Variables & Fair Investigations

Questions using confound

Problem 1

Illustrative record: Group A receives 10 mL daily and bright light; Group B receives 5 mL and dim light. After seven days, A gains 4 cm and B gains 1 cm. Identify the intended variable, measured outcome, and confound. Propose a fairer comparison and explain what the current data do establish.
Answer and explanation

The record shows a 3 cm difference in height gain, but both water and light differ. It cannot isolate water’s effect. A revised comparison would keep light, species, starting conditions, and times comparable while changing only the defined water treatment; independent seedlings and recorded variation would strengthen the evidence.

Identify water amount as the intended factor.

Measure height change in centimeters over seven days.

Recognize light as an additional changed factor.

Match light and other conditions, then use several seedlings per group.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

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