thesis - Faculty of Information and Communication Technologies ...

Chapter 6. Change Dynamics
Age (Days)
0 1,000 2,000 3,000
Age (Days)
0 1,000 2,000 3,000
N
Y
N
Y
Figure 6.3: Box plot of system maturity showing distribution of age
(in days since birth) and if the change properties hold. Graph on the
left covers Equation 6.2.9, while the right side graph covers Equation
6.2.10.
Kruskal-Wallis equality-of-populations test for the first property (Equation
6.2.9) resulted in a χ 2 value of 29.37 (with 1 degree of freedom), and
for the second property (Equation 6.2.10) resulted in a χ 2 value of 24.21
(with 1 degree of freedom). In both cases, the χ 2 value is well above the
critical level of 3.84 (1 degrees of freedom) and hence the null hypothesis
was rejected at a significance level of 0.05.
The Kruskal-Wallis test shows that system maturity has an impact, but
it does not answer a related question – Does the probability that the
stated properties hold increase with age?. That is, as software matures
does the probability of stability increase from the 80% indicated for the
first property? In order to answer this specific question, we constructed
a Logistic model [279] to predict the probability that the change properties
(Equations 6.2.9 and 6.2.10) will hold.
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