Consider again the data at the time of the first interview 1daycode = 12 for participants in the HEI-2005 study (Guenther et al. 2007). Find a 95% confidence interval estimate of the difference in the mean HEI-2005 scores between participants in the HEI study who smoke and those who do not smoke. The data is stored in the data file HEI Cost Data Variable Subset.
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