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Solved: Accuracy of software effort estimates.
Chapter 12, Problem 114E(choose chapter or problem)
Problem 114E
Accuracy of software effort estimates. Periodically, software engineers must provide estimates of their effort indeveloping new software. In the Journal of EmpiricalSoftware Engineering (Vol. 9, 2004), multiple regressionwas used to predict the accuracy of these effort estimates.The dependent variable, defined as the relative error inestimating effort,
y = (Actual effort - Estimated effort)/(Actual effort)
was determined for each in a sample of n = 49 softwaredevelopment tasks. Eight independent variables wereevaluated as potential predictors of relative error usingstepwise regression. Each of these was formulated as adummy variable, as shown in the table.
a. In step 1 of the stepwise regression, how many different one-variable models are fit to the data?
b. In step 1, the variable x1 is selected as the best one-variable predictor. How is this determined?
c. In step 2 of the stepwise regression, how many different two-variable models (where x1 is one of thevariables) are fit to the data?
d. The only two variables selected for entry into the stepwise regression model were x1 and x8. The stepwiseregression yielded the following prediction equation:
Give a practical interpretation of the β estimates multiplied by x1 and x8.
e. Why should a researcher be wary of using the model,part d, as the final model for predicting effort (y)?
Questions & Answers
QUESTION:
Problem 114E
Accuracy of software effort estimates. Periodically, software engineers must provide estimates of their effort indeveloping new software. In the Journal of EmpiricalSoftware Engineering (Vol. 9, 2004), multiple regressionwas used to predict the accuracy of these effort estimates.The dependent variable, defined as the relative error inestimating effort,
y = (Actual effort - Estimated effort)/(Actual effort)
was determined for each in a sample of n = 49 softwaredevelopment tasks. Eight independent variables wereevaluated as potential predictors of relative error usingstepwise regression. Each of these was formulated as adummy variable, as shown in the table.
a. In step 1 of the stepwise regression, how many different one-variable models are fit to the data?
b. In step 1, the variable x1 is selected as the best one-variable predictor. How is this determined?
c. In step 2 of the stepwise regression, how many different two-variable models (where x1 is one of thevariables) are fit to the data?
d. The only two variables selected for entry into the stepwise regression model were x1 and x8. The stepwiseregression yielded the following prediction equation:
Give a practical interpretation of the β estimates multiplied by x1 and x8.
e. Why should a researcher be wary of using the model,part d, as the final model for predicting effort (y)?
ANSWER:
Step 1 of 5
(a)
The dependent variable is the relative error in estimating effort.
There are 8 independent variables involved in the model, which are given below:
1. Company role of estimator
2. Task complexity
3. Contract type
4. Customer importance
5. Customer priority
6. Level of knowledge
7. Participation
8. Previous accuracy
Therefore, there are 8 different one-variable models fitted to the data.