Build a fair comparison, then test whether the result can rule out a competing explanation.
Map the decision
A lab compares a gel applied to cut flowers with no gel. Begin by naming the outcome it can measure, such as hours before wilting. Then identify what changes between groups. If application adds water, the comparison needs the same amount of water and the same handling.
A fixed condition such as vase size is not itself the comparison group. The group provides a baseline response under shared conditions.
Read a result under its design
Suppose a gel group lasts longer but stands farther from a heating vent. Heat could change wilting independently. Give both treatments to flowers near each vent setting and compare them under the same setting.
To check whether the explanation transfers, ask which variables could vary in the next location. A narrow conclusion from one temperature is more defensible than a claim about all rooms.
Apply the guide
Two lamps are tested, each in a different room. Why do more plants in those same rooms leave a problem?Reveal explanation
Lamp and room still vary together. Compare both lamps in each room or hold room conditions alike.
A foam is dissolved in water before it is applied. What does the comparison receive?Reveal explanation
The same handling and volume of water, without the foam.
Turn the idea into practice.
Apply the rule to a new case, then explain your choice.
Practice this skillSources & authorship
Sources support scientific principles. Practice scenarios and teaching examples are original.
Original OpenExam guide
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OpenStax Biology 2e 1.1 The Science of Biology