PROTEUS

              

 

 

 

 

 

 

 

Back to ENH440 Problems & Solutions

 

Solution in detail.......page 27 "A"

 Ho1  :  no difference between location in terms of bites/hr (A = B)

 Ho2  : no difference between repellents in terms of bites/hr  (C = D = N)

 Ho3 : no interaction between these main effects in terms of bites/hr

 source of    sum of     degrees of      mean      F ratio        P

 variation    squares     freedom        square                       

 ~~~~~~~~    ~~~~~~     ~~~~~~~~~     ~~~~~~~    ~~~~~~     ~~~~~~~~~

 all groups     330                 5       

 location       202                 1           202          22.96         <<0.01 

 repellent     112                 2             56            6.37         <0.01

 LxR inter      16                  2              8            0.91         >0.05 ns

 residual      475                 54              8.796

 Total          805                 59   

 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 Interaction F ratio =  MS(inter)÷ MS(resid)  = 0.91     

                                      F(0.05, 2,54df) >3.15    .... unable to reject Ho      

                            

 Location F ratio =  MS(locat)÷ MS(resid)  = 22.96     

                                      F(0.01, 1,54df) >7.08       .... reject Ho  

 

 Repellent F ratio =  MS(repel)÷ MS(resid)  = 6.37     

                                      F(0.01, 2,54df) >4.98       .... reject Ho  

 

 

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      C         D         N

          WETLANDS

      C        D         N

              FOREST

 

     W                F

           Control

     W                 F

            DEET

     W                 F

            NEW

 

Interaction.    Very little interaction was observed (not stat.sig), so results will be reported simply for main effects without any important interaction between them.    F: 0.91, 2,54 df.  P>0.05  

 

Location.  Strong evidence that bites/hr were recorded a much higher rate for wetlands (mean: 38.7) than for forest areas (mean: 14.0).  Difference is statistically significant at 0.01 and the null hypothesis can be rejected.  F: 22.96, 1,54 df. P<0.01

 

Repellent.  Strong evidence that the three materials did not have the same effect. The control group produced the highest bites/hr (mean: 42.5), roughly three times higher than the "DEET" group (mean 16).  The "new" material was positions between the two (mean: 20.5)  Difference is statistically significant at 0.01 and the null hypothesis can be rejected.  F: 6.37, 2,54 df. P<0.01