In: Statistics and Probability
The systolic blood pressure of 16 students was measured before a test. The blood pressure from this sample averaged 165, with a standard deviation of 40.
a) Compute the approximate 95% confidence interval for mean systolic blood pressure, and make a sketch illustrating these confidence intervals
b) If a mean blood pressure above 130 is considered “stressed”, what do your calculations show regarding the probability that the observed mean is above the “stressed” level.
Level of Significance ,    α =    0.05
sample std dev ,    s =    40
Sample Size ,   n =    16
Sample Mean,    x̅ =   165
a) degree of freedom=   DF=n-1=  
15  
't value='   tα/2=   2.1314   [Excel
formula =t.inv(α/2,df) ]
          
Standard Error , SE =   s/√n =  
10.0000  
margin of error ,   E=t*SE =  
21.3145  
95% confidence interval is       
   
Interval Lower Limit=   x̅ - E =   
143.6855  
Interval Upper Limit=   x̅ + E =   
186.3145  
we are 95% confident that true mean systolic blood pressure lies within confidence interval.
b)
confidence interval is above 130,so, observed mean is above stressed level