Ascaridia galli is a parasitic roundworm that attacks the intestines of birds, especially chickens and turkeys. Scientists are working on a synthetic vaccine (antigen) for the parasite. The success of the vaccine hinges on the characteristics of DNA in peptide (protein) produced by the antigen. In the journal Gene Therapy and Molecular Biology (June 2009), scientists tested alleles of antigen-produced protein for level of peptide. For a sample of 4 alleles, the mean peptide score was 1.43 and the standard deviation was .13.

a. Use this information to construct a 90% confidence interval for the true mean peptide score in alleles of the antigen-produced protein.

b. Interpret the interval for the scientists.

c. What is meant by the phrase "90% confidence"?