TABLE 18-8
Recently, a University Switched to a New

question 64

Short Answer

TABLE 18-8
Recently, a university switched to a new type of computer-based registration. The registrar is concerned with the amount of time students are spending on the computer registering under the new system. She decides to randomly select 8 students on each of the 12 days of the registration and determine the time each spends on the computer registering. The range, mean, and standard deviation of the times required to register are in the table that follows.
$$\begin{array} { c c l l } \text { Day } & \text { Range } & \text { Mean } & \text { Std.Dev. } \\1 & 10 & 5.250 & 3.4949 \\2 & 31 & 15.250 & 10.3060 \\3 & 13 & 20.375 & 4.9262 \\4 & 21 & 22.875 & 8.3911 \\5 & 35 & 8.500 & 11.3767 \\6 & 18 & 7.875 & 6.9372 \\7 & 25 & 11.250 & 8.5815 \\8 & 30 & 7.875 & 9.5235 \\9 & 17 & 10.250 & 6.3640 \\10 & 22 & 9.500 & 7.8740 \\11 & 27 & 7.875 & 8.7086 \\12 & 26 & 12.875 & 9.3723\end{array}$$
-Referring to Table 18-8, an $\bar{X }$ chart is to be used for the time required to register. One way to obtain the control limits is to take the grand mean and add and subtract the product of A2 times the average of the sample ranges. For this data set, the value of A2 is ______.

---

Definitions:

Systematic Variance

The part of variance in a set of data that is attributable to identified sources or factors, as opposed to random or error variance.

Error Variance

Random variability in a set of scores that is not the result of the independent variable. Statistically, the variability of each score from its group mean.

Between-Groups Variance

captures the differences in means across different groups in an experiment, reflecting how much group members vary from each other overall.

Within-Group Variance

The variation of observations within a single group or category, measuring how much individual scores differ from the mean of that group.