Mariah is carrying out a research to understand the effect of obesity on stress levels in female participants above the age of 40. She classified the participants into ­subsamples of the age groups 40...

Mariah is carrying out a research to understand the effect of obesity on stress levels in female participants above the age of 40. She classified the participants into ­subsamples of the age groups 40 to 50, 50 to 60, and 60 to 70. She then happened to read the recommendation of Maxwell and Delaney in this regard and decided to use ­statistical control rather than categorize people into three groups. What exactly did Mariah decide to do in her sampling process?

a.            She isolated the variation caused by the extraneous variable.

b.            She left the variable of age in its natural unit and used it only during data analysis.

c.             She categorized women according to their weight instead.

d.            She negated the influence of weight in the experiment.

e.            She included weight as an additional variable.