Psychologist is interested in how early childhood nutrition affects height. To research this subject he tracks the nutritional consumption and growth of the same group of infants from age 1 through age 6. This research technique is utilizing a design

Longitudinal Design of research.

Explanation:

The psychologist is comparing the effects of nutrition on height and so he tracks the nutritional consumption and growth of same group of infants from age 1 to age 6. This means that he made repeated observation for the same variable in  same sample in order to trace the growth rate.

This design of research according to which a conclusion is derived after making repeated observation of same variable, is classified as Longitudinal design of research.

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colors do exist. the color of the sky is actually violet; humans percieve the color of the sky as blue.