Ecological researchers measured the concentration of red cells in the blood of 2

Question

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 material parasite Plasmodium. The red cell counts (10^-3 Times cells per mm^3) were as reported in the table.^37 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 alpha = 0.05 alpha = 0.10

Explanation / Answer

a)

Formulating the null and alternative hypotheses,              
              
Ho:   u1 - u2   <=   0  
Ha:   u1 - u2   >   0  
At level of significance =    0.05          
As we can see, this is a    right   tailed test.      
Calculating the means of each group,              
              
X1 =    972.1          
X2 =    843.4          
              
Calculating the standard deviations of each group,              
              
s1 =    245.1          
s2 =    251.2          
              
Thus, the standard error of their difference is, by using sD = sqrt(s1^2/n1 + s2^2/n2):              
              
n1 = sample size of group 1 =    12          
n2 = sample size of group 2 =    15          

df = 24 [given]

Also, sD =    95.98400995          
              
Thus, the t statistic will be              
              
t = [X1 - X2 - uD]/sD =    1.340848336          
              
where uD = hypothesized difference =    0          
              
Also, using p values,              
              
p = 0.096261753
              
              
As P > 0.05,    WE FAIL TO REJECT THE NULL HYPOTHESIS.

Hence, there is no significant evidence at 0.05 level that the infected animals have a lower red cell count. [CONCLUSION]

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b)

As
              
p = 0.096261753
              
              
As P < 0.10,    WE REJECT THE NULL HYPOTHESIS.

Hence, there is significant evidence at 0.10 level that the infected animals have a lower red cell count. [CONCLUSION]

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Hi! There seems to be a problem with the table, as the mean of noninfected animals is actually the one which is lower. Please report this to your instructor. Thanks!

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