Table H.1
A worker was observed for four cycles in a repetitive task that contains four distinct elements. The observer recorded the following items in seconds, using the snap-back method:

-How many more observations must be made in order to estimate the select time for Element 1 if the company wishes to be within 6% of the actual value with 95% confidence?
A) 81
B) 67
C) 53
D) 48

Question

Table H.1
A worker was observed for four cycles in a repetitive task that contains four distinct elements. The observer recorded the following items in seconds, using the snap-back method:
 
-How many more observations must be made in order to estimate the select time for Element 1 if the company wishes to be within 6% of the actual value with 95% confidence?
A) 81 
B) 67 
C) 53 
D) 48

Quizplus · Accepted Answer

In order to estimate the select time for Element 1 within 6% of the actual value with 95% confidence, we need to use the formula n = (Z^2 * σ^2) / E^2, where n is the sample size, Z is the Z-value for the desired confidence level (1.96 for 95% confidence), σ is the standard deviation of the observations, and E is the desired margin of error (6% in this case, which is equivalent to 0.06). We can estimate σ as the range of the observations divided by 6 (since there are 4 distinct elements, each element should be observed on average once per cycle, and we want to estimate the standard deviation for a single observation). The range of the observations is 4.47 seconds (16.87 - 12.40). Thus, σ is approximately equal to 0.75 seconds. Plugging these values into the formula, we get n = (1.96^2 * 0.75^2) / 0.06^2, which is approximately equal to 48. Therefore, we need to make 48 more observations to estimate the select time for Element 1 with the desired level of precision and confidence.

Table H.1 A Worker Was Observed for Four Cycles in a Repetitive