Assume that REM (rapid eye movement) sleep time is normally distributed for both children and adults. A random sample of n1 = 10 children (9 years old) showed that they had an average REM sleep time of
x1 = 2.8
hours per night. From previous studies, it is known that σ1 = 0.7 hour. Another random sample of n2 = 10 adults showed that they had an average REM sleep time of
x2 = 2.1
hours per night. Previous studies show that σ2 = 0.6 hour. Note: If a two-sample t-test is appropriate, for degrees of freedom d.f. not in the Student's t table, use the closest d.f. that is smaller. In some situations, this choice of d.f. may increase the P-value by a small amount and therefore produce a slightly more "conservative" answer.
What is the value of the sample test statistic?