biostatistics

1.5.5 Ecological researchers measured the concentration of red cells in the blood of 27 field-caught lizards (Sceloporus occideritalis). In addition, they examined each lizard for infection by the malarial parasite Plasmodium. The red cell counts (10-* x cells per mm) were as reported in the table 37 Infected animals Noninfected animals n 12 15 972.1 843.4 S 245.1 251.2 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 distrib- uted. 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) a = 0.05 (b) a = 0.10 [Note: Formula (6.7.1) yields 24 df.]