Question

A researcher studied a group of identical twins who had been separated and adopted at birth. In each case, one twin (Twin A) was adopted by a low-income family and the other (Twin B) by a high-income family. Both twins were given an IQ test as adults. Here are their scores:

IQ and income (1.3) Do identical twins living in low-income homes tend to have lower IQs later in

life than their twins who live in high-income homes? Give appropriate evidence to support your answer.

Short answer

There is evidence that identical twins from low-income families have lower IQs later in life than their high-income counterparts.

Step-by-step solution

Given information

Twin A:	120	99	99	94	111	97	99	94	104	114	113	100
Twin B:	128	104	108	100	116	105	100	100	103	124	114	112

Concept

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.

Explanation

According to the question, a researcher looked into a group of identical twins who had been separated and adopted at infancy. As a result, we'll calculate the mean for both twins as follows: $$\begin{gathered} \overline{x_A}=\frac{120+99+....+113+100}{12} \\ =103.6667 \end{gathered}$$

$$\begin{gathered} {\overline{x}}_B=\frac{128+104+....+114+112}{12} \\ =109.5 \end{gathered}$$

The difference in IQ scores is around five points, however since the sample size is only $12$, this variation could be attributable to chance. As a result, we can infer that there is no statistically significant evidence that identical twins from low-income families have lower IQs later in life than their high-income counterparts.