HP HP12C hp 12c_user's guide_English_E_HDPMBF12E44.pdf - Page 80

80 Section 6: Statistics Functions Linear Estimation With two-variable statistical data accumulated in the statistics registers, you can estimate a new y-value ( yˆ ) given a new x-value, and estimate a new x-value ( xˆ ) given a new y-value. To calculate yˆ : 1. Key in a new x-value. 2. Press gR. To calculate xˆ : 1. Key in a new y-value. 2. Press gQ. Example: Using the accumulated statistics from the preceding problem, estimate the amount of sales delivered by a new salesperson working 48 hours per week. Keystrokes 48gQ Display 28,818.93 Estimated sales for a 48 hour workweek. The reliability of a linear estimate depends upon how closely the data pairs would, if plotted on a graph, lie in a straight line. The usual measure of this reliability is the correlation coefficient, r. This quantity is automatically calculated whenever yˆ or xˆ is calculated; to display it, press ~. A correlation coefficient close to 1 or -1 indicates that the data pairs lie very close to a straight line. On the other hand, a correlation coefficient close to 0 indicates that the data pairs do not lie closely to a straight line; and a linear estimate using this data would not be very reliable. Example: Check the reliability of the linear estimate in the preceding example by displaying the correlation coefficient. Keystrokes ~ Display 0.90 The correlation coefficient is close to 1, so the sales calculated in the preceding example is a good estimate. To graph the regression line, calculate the coefficients of the linear equation y = A + Bx. 1. Press 0gR to compute the y-intercept (A). 2. Press 1gR~d~- to compute the slope of the line (B). File name: hp 12c_user's guide_English_HDPMBF12E44 Printered Date: 2005/7/29 Page: 80 of 209 Dimension: 14.8 cm x 21 cm