Chapter 8 Nonlinear Regression Functions
2 Nonlinear Regression Functions (SW Chapter 8)
3 The TestScore – STR relation looks linear (maybe)…
4 But the TestScore – Income relation looks nonlinear...
5 Nonlinear Regression Population Regression Functions – General Ideas (SW Section 8.1)
6 The general nonlinear population regression function
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8 Nonlinear Functions of a Single Independent Variable (SW Section 8.2)
9 1. Polynomials in X
10 Example: the TestScore – Income relation
11 Estimation of the quadratic specification in STATA
12 Interpreting the estimated regression function:
13 Interpreting the estimated regression function, ctd:
14
15 Estimation of a cubic specification in STATA
16
17 Summary: polynomial regression functions
18 2. Logarithmic functions of Y and/or X
19 The three log regression specifications:
20 I. Linear-log population regression function
21 Linear-log case, continued
22 Example: TestScore vs. ln(Income)
23 The linear-log and cubic regression functions
24 II. Log-linear population regression function
25 Log-linear case, continued
26 III. Log-log population regression function
27 Log-log case, continued
28 Example: ln( TestScore) vs. ln( Income)
29 Example: ln( TestScore) vs. ln( Income), ctd.
30 The log-linear and log-log specifications:
31 Summary: Logarithmic transformations
32 Other nonlinear functions (and nonlinear least squares) (SW App. 8.1)
33 Negative exponential growth
34 Nonlinear Least Squares
35
36
37 Interactions Between Independent Variables (SW Section 8.3)
38 (a) Interactions between two binary variables
39 Interpreting the coefficients
40 Example: TestScore, STR, English learners
41 (b) Interactions between continuous and binary variables
42 Binary-continuous interactions: the two regression lines
43 Binary-continuous interactions, ctd.
44 Interpreting the coefficients
45 Example: TestScore, STR, HiEL (=1 if PctEL 10)
46 Example, ctd: Testing hypotheses
47 (c) Interactions between two continuous variables
48 Interpreting the coefficients:
49 Example: TestScore, STR, PctEL
50 Example, ctd: hypothesis tests
51 Application: Nonlinear Effects on Test Scores of the Student-Teacher Ratio (SW Section 8.4)
52 Strategy for Question #1 (different effects for different STR?)
53 Strategy for Question #2 (interactions between PctEL and STR?)
54 What is a good “base” specification?
55
56 Tests of joint hypotheses:
57 Interpreting the regression functions via plots:
58 Next, compare the regressions with interactions:
59 Summary: Nonlinear Regression Functions