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Solved: Accuracy of software effort estimates. Refer to
Chapter 12, Problem 148SE(choose chapter or problem)
Accuracy of software effort estimates. Refer to theJournal of Empirical Software Engineering (Vol.9, 2004) study of the accuracy of software effort estimates, Exercise 12.73 (p. 712). Recall that the dependent variable (y) is measured as relative error of the effort estimate of a software development task. A total of eight independent variables were evaluated as potential predictors of relative error. Each of these was formulated as a dummy variable, as shown in the table below.
a. The eight independent variables were entered into a stepwise regression, and the following two variables were selected for entry into the model: \(x_1\) and \(x_8\).Write the main effects model for E(y) as a function of these two variables.
b. The stepwise regression yielded the following prediction equation:
\(\hat{y}=.12-.28 x_{1}+.27 x_{8}\)
Give a practical interpretation of the \(\beta\) estimates multiplied by \(x_1\) and \(x_8\).
c. The researcher is concerned that the sign of \(\hat{\beta}_1\) in the model is the opposite from what is expected. (Theresearcher expects a project leader to have a smaller relative error of estimation than a developer.) Give atleast one reason why this phenomenon occurred.
Questions & Answers
QUESTION:
Accuracy of software effort estimates. Refer to theJournal of Empirical Software Engineering (Vol.9, 2004) study of the accuracy of software effort estimates, Exercise 12.73 (p. 712). Recall that the dependent variable (y) is measured as relative error of the effort estimate of a software development task. A total of eight independent variables were evaluated as potential predictors of relative error. Each of these was formulated as a dummy variable, as shown in the table below.
a. The eight independent variables were entered into a stepwise regression, and the following two variables were selected for entry into the model: \(x_1\) and \(x_8\).Write the main effects model for E(y) as a function of these two variables.
b. The stepwise regression yielded the following prediction equation:
\(\hat{y}=.12-.28 x_{1}+.27 x_{8}\)
Give a practical interpretation of the \(\beta\) estimates multiplied by \(x_1\) and \(x_8\).
c. The researcher is concerned that the sign of \(\hat{\beta}_1\) in the model is the opposite from what is expected. (Theresearcher expects a project leader to have a smaller relative error of estimation than a developer.) Give atleast one reason why this phenomenon occurred.
ANSWER:
Step 1 of 3
The eight independent dummy variables are considered to study the accuracy of the software effort estimate.
a) We need to write the main effect model for E (y) as a function of the two
variables 
The main effect model involves 
