User manual SPSS REGRESSION MODELS 11.0

[. . . ] SPSS Regression Models 11. 0 TM For more information about SPSS® software products, please visit our Web site at http://www. spss. com or contact SPSS Inc. 233 South Wacker Drive, 11th Floor Chicago, IL 60606-6412 Tel: (312) 651-3000 Fax: (312) 651-3668 SPSS is a registered trademark and the other product names are the trademarks of SPSS Inc. No material describing such software may be produced or distributed without the written permission of the owners of the trademark and license rights in the software and the copyrights in the published materials. Use, duplication, or disclosure by the Government is subject to restrictions as set forth in subdivision (c)(1)(ii) of The Rights in Technical Data and Computer Software clause at 52. 227-7013. [. . . ] The values of this variable cannot be negative and cannot be less than the values of the response frequency variable for each case. If you do, click Define Range to define the groups. Select one or more covariate(s). This variable contains the level of the stimulus applied to each observation. If you want to transform the covariate, select a transformation from Probit Analysis 19 the Transform drop-down list. If no transformation is applied, and there is a control group, then the control group is included in the analysis. Select either Probit or Logit model. Probit Analysis Define Range Figure 4. 2 Probit Analysis Define Range dialog box This allows you to specify the levels of the factor variable that will be analyzed. The factor levels must be coded as consecutive integers, and all levels in the range you specify will be analyzed. Probit Analysis Options Figure 4. 3 Probit Analysis Options dialog box 20 Chapter 4 You can specify options for your probit analysis: Statistics. Allows you to request the following optional statistics: Frequencies, Relative median potency, Parallelism test, and Fiducial confidence intervals. Fiducial confidence intervals and Relative median potency are unavailable if you have selected more than one covariate. Relative median potency and Parallelism test are available only if you have selected a factor variable. Allows you to indicate a natural response rate even in the absence of the stimulus. Allows you to control parameters of the iterative parameter-estimation algorithm. You can override the defaults for maximum iterations, step limit, and optimality tolerance. PROBIT Command Additional Features The SPSS command language also allows you to: · Request an analysis on both the probit and logit models. · Transform the covariates by bases other than base 10 or natural log. 5 Nonlinear Regression Nonlinear regression is a method of finding a nonlinear model of the relationship between the dependent variable and a set of independent variables. Unlike traditional linear regression, which is restricted to estimating linear models, nonlinear regression can estimate models with arbitrary relationships between independent and dependent variables. Note that this procedure is not necessary for simple polynomial models of the form Y = A + BX**2 . By defining W = X**2 , we get a simple linear model, Y = A + BW , which can be estimated using traditional methods such as the Linear Regression procedure. Constrained nonlinear regression uses the algorithms proposed and implemented in NPSOL® by Gill, Murray, Saunders, and Wright to estimate the model parameters. A scatterplot shows that there seems to be a strong relationship between population and time, but the relationship is nonlinear, so it requires the special estimation methods of the Nonlinear Regression procedure. By setting up an appropriate equation, such as a logistic population growth model, we can get a good estimate of the model, allowing us to make predictions about population for times that were not actually measured. For each model: sum of squares for regression, residual, uncorrected total and corrected total, parameter estimates, asymptotic standard errors, and asymptotic correlation matrix of parameter estimates. Categorical variables such as religion, major, or region of residence need to be recoded to binary (dummy) variables or other types of contrast variables. Results are valid only if you have specified a function that accurately describes the relationship between dependent and independent variables. [. . . ] The first degree of freedom contains the linear effect across all categories; the second degree of freedom, the quadratic effect; the third degree of freedom, the cubic; and so on for the higher-order effects. You can specify the spacing between levels of the treatment measured by the given categorical variable. Equal spacing, which is the default if you omit the metric, can be specified as consecutive integers from 1 to k, where k is the number of categories. If the variable drug has three categories, the subcommand /CONTRAST(DRUG)=POLYNOMIAL is the same as /CONTRAST(DRUG)=POLYNOMIAL(1, 2, 3) Equal spacing is not always necessary, however. [. . . ]