After running a simulation in forecast charts, you can determine the probability of occurrence called confidence intervals ; that is, given two values, what are the chances that the outcome will fall between these two values? Figure 4-12 illustrates that there is a 90 percent probability that the final outcome (in this case, the level of income) will be between $0.2781 and $1.3068. The two-tailed confidence interval can be obtained by first selecting Two-Tail as the type, entering the desired certainty value (e.g., 90), and hitting Tab on the keyboard. The two computed values corresponding to the certainty value will then be displayed. In this example, there is a 5 percent probability that income will be at or below $0.2781 and another 5 percent probability that income will be at or above $1.3068; that is, the two-tailed confidence interval is a symmetrical interval centered on the median or 50th percentile value. Thus, both tails will have the same probability.

Alternatively, a one-tail probability can be computed. Figure 4-13 shows a Left-Tail selection at 95 percent confidence (i.e., choose Left-Tail as the type, enter 95 as the certainty level, and hit Tab on the keyboard). This means that there is a 95 percent probability that the income will be below $1.3068 (i.e., 95% on the left tail of $1.3068) or a 5% probability that income will be at or above $1.3068, corresponding perfectly with the results seen in Figure...