Maffulli et al. studied the effectiveness of early weightbearing and ankle mobil

Question

Maffulli et al. studied the effectiveness of early weightbearing and ankle mobilization therapies following acute repair of a ruptured Achilles tendon. One of the variables they measured following treatment was the isometric gastrocsoleus muscle strength. In 19 subjects, the mean isometric strength for the operated limb (in Newtons) was 250.8 with a sample standard deviation of 130.9. We assume that these 19 patients constitute a random sample from a population of similar subjects. We also assume that the population values are approximately normally distributed. Find the UPPER confidence limit for a 95% confidence interval for .

1. 313.65

2. 313.89

3. 314.1

4. 309.66

Explanation / Answer

Note that              
      
Upper Bound = X + t(alpha/2) * s / sqrt(n)              
              
where              
alpha/2 = (1 - confidence level)/2 =    0.025          
X = sample mean =    250.8          
t(alpha/2) = critical t for the confidence interval =    2.10092204          
s = sample standard deviation =    130.9          
n = sample size =    19          
df = n - 1 =    18          
Thus,              

Upper bound =    313.8917804 = 313.89 [ANSWER, OPTION 2]          
              

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