A nurse was hired by a governmental ecology agency to investigate the impact of a lead smelter on the level of lead in the blood of children living near the smelter. Ten children were chosen at random from those living near the smelter. A comparison group of seven children was randomly selected from those living in an area relatively free from possible lead pollution. Blood samples were taken from the children and lead levels determined. The following are the results (scores are in micrograms of lead per 100 milliliters of blood. Lead Levels Children living near smelter Children living in unpolluted area 18 9 16 13 21 8 14 15 17 17 19 12 22 11 24 15 18 What is the null hypothesis? The distance one lives from a lead smelter has no effect on the level of lead in the blood of children What is the alternative hypothesis? The distance one lives from a lead smelter has an effect on the level of lead in the blood of children What is the value of t obtained assuming homogeneity of variance? What is the value of t-critical α = 0.05 2 tail? What might the candidate conclude using α = 0.05 2 tail? What type error might the candidate have made? Estimate the size of the real effect using omega squared and cohen’s d. ώ2 = tobt2 -1 tobt2 +N-1 ώ2 = Cohen’s d Estimated d = Xbar1-Xbar2 Spooled Spooled=the square root of the pooled variance sp2= SS1+SS2 = SS1 = n1+n2-2 SS2 = Spooled = Estimated d = Do you satisfy the assumption of homogeneity of variance? How do you know? Why is the t-test assuming homogeneity of variance computed with more df than the one computed assuming heterogeneity of variance.
A nurse was hired by a governmental ecology agency to investigate the impact of a lead smelter on the level of lead in the blood of children living near the smelter. Ten children were chosen at random from those living near the smelter. A comparison group of seven children was randomly selected from those living in an area relatively free from possible lead pollution. Blood samples were taken from the children and lead levels determined. The following are the results (scores are in micrograms of lead per 100 milliliters of blood.
Lead Levels
Children living near smelter Children living in unpolluted area
18 9
16 13
21 8
14 15
17 17
19 12
22 11
24
15
18
What is the null hypothesis? The distance one lives from a lead smelter has no effect on the level of lead in the blood of children
What is the alternative hypothesis? The distance one lives from a lead smelter has an effect on the level of lead in the blood of children
What is the value of t obtained assuming homogeneity of variance?
What is the value of t-critical α = 0.05 2 tail?
What might the candidate conclude using α = 0.05 2 tail?
What type error might the candidate have made?
Estimate the size of the real effect using omega squared and cohen’s d.
ώ2 = tobt2 -1
tobt2 +N-1
ώ2 =
Cohen’s d
Estimated d = Xbar1-Xbar2
Spooled
Spooled=the square root of the pooled variance
sp2= SS1+SS2 = SS1 =
n1+n2-2 SS2 =
Spooled =
Estimated d =
Do you satisfy the assumption of homogeneity of variance? How do you know?
Why is the t-test assuming homogeneity of variance computed with more df than the one computed assuming heterogeneity of variance.
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