Dr. Susan Sweeney, a Providence, Rhode Island, psychologist, specializes in treating patients who are agoraphobic (i.e., afraid to leave their homes). The following table indicates how many patients Dr. Sweeney has seen each year for the past 10 years. It also indicates what the robbery rate was in Providence during the same year:
.:.
Using trend analysis, predict the number of patients Dr. Sweeney will see in years 11 and 12 as a function of time. How well does the model fir the data?
SOLUTION:
| Year X | Year X | Patients Y | Patients Y | Patients Y | X2 | X2 | X2 | Y2 | Y2 | Y2 | XY | XY | XY |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 1 | 36 | 36 | 36 | 1 | 1 | 1 | 1,296 | 1,296 | 1,296 | 36 | 36 | 36 |
| 2 | 2 | 33 | 33 | 33 | 4 | 4 | 4 | 1,089 | 1,089 | 1,089 | 66 | 66 | 66 |
| 3 | 3 | 40 | 40 | 40 | 9 | 9 | 9 | 1,600 | 1,600 | 1,600 | 120 | 120 | 120 |
| 4 | 4 | 41 | 41 | 41 | 16 | 16 | 16 | 1,681 | 1,681 | 1,681 | 164 | 164 | 164 |
| 5 | 5 | 40 | 40 | 40 | 25 | 25 | 25 | 1,600 | 1,600 | 1,600 | 200 | 200 | 200 |
| 6 | 6 | 55 | 55 | 55 | 36 | 36 | 36 | 3,025 | 3,025 | 3,025 | 330 | 330 | 330 |
| 7 | 7 | 60 | 60 | 60 | 49 | 49 | 49 | 3,600 | 3,600 | 3,600 | 420 | 420 | 420 |
| 8 | 8 | 54 | 54 | 54 | 64 | 64 | 64 | 2,916 | 2,916 | 2,916 | 432 | 432 | 432 |
| 9 | 9 | 58 | 58 | 58 | 81 | 81 | 81 | 3,364 | 3,364 | 3,364 | 522 | 522 | 522 |
| 10 | 10 | 61 | 61 | 61 | 100 | 100 | 100 | 3,721 | 3,721 | 3,721 | 610 | 610 | 610 |
| 55 | 478 | 385 | 23,892 | 2,900 |
Given: Y = a + bX where:
And X = 55, Y = 478, XY = 2900, X2 = 385, Y2 = 23892, Then:
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