  Defining strategies on how to perform quality assurance (QA) and how to
control such activities is a challenging task for organizations developing or
maintaining software and software-intensive systems. Planning and adjusting QA
activities could benefit from accurate estimations of the expected defect
content of relevant artifacts and the effectiveness of important quality
assurance activities. Combining expert opinion with commonly available
measurement data in a hybrid way promises to overcome the weaknesses of purely
data-driven or purely expert-based estimation methods. This article presents a
case study of the hybrid estimation method HyDEEP for estimating defect content
and QA effectiveness in the telecommunication domain. The specific focus of
this case study is the use of the method for gaining quantitative predictions.
This aspect has not been empirically analyzed in previous work. Among other
things, the results show that for defect content estimation, the method
performs significantly better statistically than purely data-based methods,
with a relative error of 0.3 on average (MMRE).
