Question 6.88
53. Major recalls of toys with lead paint refocused people on the dangers of lead exposure. Below are data from research exploring the association with student achievement for blood lead levels below the “danger threshold” of 10 mcg/dl set by the Centers for Disease Control [M. L. Miranda et al., The relationship between early childhood blood lead levels and performance on end-of-grade tests, Environmental Health Perspectives, 115 (2007): 1242–1247].
| Blood lead level | 1 | 2 | 3 | 4 | 5 |
| Mean fourth-grade reading score | 255.9 | 253.8 | 252.6 | 251.0 | 250.4 |
| Blood lead level | 6 | 7 | 8 | 9 | |
| Mean fourth-grade reading score | 249.5 | 248.5 | 247.8 | 249.3 |
- What are the explanatory and response variables?
- Do you expect a positive or negative association between these variables? Why? Does the scatterplot support your answer?
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Figure 6.24: Figure 6.24 IQ and reading test scores for 60 fifth-grade children, for Exercise 54.
53.
(a) Lead level is the explanatory variable; reading score is the response variable.
(b) Negative; sample response: Due to lead being toxic, expect that increases in lead levels will affect children’s brains and impede reading; yes, the scatterplot supports this answer.