1 A clinical trial is run to compare the effectiveness of an

1) A clinical trial is run to compare the effectiveness of an experimental drug in reducing preterm delivery to a drug considered standard care and to placebo. Pregnant women are enrolled and randomly assigned to receive the experimental drug, the standard drug, or placebo. Women are followed through delivery and classified as delivering preterm (< 37 weeks) or not. The resulting data are shown below.

Preterm Delivery

Experimental Drug

Standard Drug

Placebo

Yes

17

23

35

No

83

77

65

Is there a statistically significant difference in the proportions of women delivering preterm among the three treatment groups? Run the test at a 5 percent level of significance.

Solution

1.

Doing an Expected Value Chart,          
          
25   25   25  
75   75   75  
          
Using chi^2 = Sum[(O - E)^2/E],          
          
chi^2 =    8.96      
          
With df = (a - 1)(b - 1), where a and b are the number of categories of each variable,          
          
a =    3      
b =    2      
          
df =    2      
          
Thus, the critical value is          
          
significance level =    0.05      
          
chi^2(critical) =    5.991464547      
          
Also, the p value is          
          
P =    0.011333413      
          
As chi^2 > 5.9915, and P < 0.05, we   REJECT THE NULL HYPOTHESIS.      
          
Thus, there is a statistically significant difference in the proportions of women delivering preterm among the three treatment groups at 0.05 level. [CONCLUSION]