6.2.         Accuracy of software effort estimates. Periodically, software engineers must provide estimates of their effort in developing new software. In the Journal of Empirical Software Engineering (Vol. 9, 2004), multiple regression was used to predict the accuracy of these effort estimates. The dependent variable, defined as the relative error in estimating effort,

 

y = (Actual effort − Estimated effort)/ (Actual effort)

was determined for each in a sample of n = 49 software development tasks. Eight independent variables  were  evaluated  as  potential predictors

of relative error using stepwise regression. Each of these was formulated as a dummy variable, as shown below.

Company role of estimator: x1 = 1 if developer, 0 if project   leader

Task complexity: x2 = 1 if low, 0 if medium/high Contract type: x3 = 1 if fixed price, 0 if hourly rate Customer  importance:  x4  = 1  if  high,  0  if   low/

medium

 

of the variables) are fit to the data?

(d)    The only two variables selected for entry into the stepwise regression model were x1 and x8. The stepwise regression yielded the following prediction equation:

yˆ    = .12 − .28x1  + .27x8

Give a practical interpretation of the β esti- mates 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)?