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A Researcher Does a Study Examining the Effects of a Preschool

question 97

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A researcher does a study examining the effects of a preschool program. He uses a nonequivalent comparison-group design. He finds that the cognitive growth of his experimental group is greater than that of his control. Unfortunately, he later finds that in general children who live in the area where he drew his experimental group tend to grow faster cognitively than children who were from the area where he drew his control group. When he discovered this problem, he discovered what threat to the internal validity of his study?


Definitions:

Reaction Rate

The speed at which reactants are converted into products in a chemical reaction.

Reaction Measurement

The process of quantifying the progress, rate, or yield of a chemical reaction using various methods like spectroscopy, calorimetry, or chromatography.

H2S

Hydrogen sulfide, a toxic, colorless gas with a characteristic odor of rotten eggs, widely found in nature and industrial processes.

Cl2

The chemical symbol for chlorine gas, a diatomic molecule consisting of two chlorine atoms, used in water purification and as a bleaching agent.

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