Ecological researchers measured the concentration of red cells in the blood of 27 field-caught lizards (Sceloporus occidetitalis). In addition, they examined each lizard for infection by the malarial parasite Plasmodium. The red cell counts (10-3 × cells per mm3) were as reported in the table.

One might expect that malaria would reduce the red cell count, and in fact previous research with another lizard species had shown such an effect. Do the data support this expectation? Assume that the data are normally distributed. Test the null hypothesis of no difference against the alternative that the infected population has a lower red cell count. Use a t test at
(a) α = 0.05
(b) α = 0.10

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Infected Noninfected animals 12 972.1 245.1 animals 15 843.4 251.2 y