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The treatments are randomly assigned to all of the experimental units in a completely randomized design.

In a double-blind experiment, neither the subjects nor the persons who interact with them and evaluate their responses are aware of the therapy they received.

Observational research looks at people and assesses factors of interest without trying to affect their responses.

Individuals are purposely subjected to a treatment in order to measure their responses in an experiment.

A researcher analyzed a group of identical twins who had been separated and adopted at birth, according to the query. As a result, using the information provided in the question, create the following scatterplot:

Twin A is on the horizontal axis and Twin B is on the vertical axis in this scatterplot. Because the scatterplot slopes upward, the variables have a positive relationship. Furthermore, the spots appear to be about centered on a line, indicating that the link is linear. Let's make a residual plot of the linear regression line now. A residual is a difference between the actual value and the linear regression line's anticipated value. As a result, it is as follows: Twin A is on the horizontal axis, while the residual is on the vertical axis, in the residual plot. Because the scatterplot shows no evident trend, the linear regression line appears to make fair predictions for Twin B's IQ values.