  The concept of software quality is very complex and has many facets.
Reflecting all these facets and at the same time measuring everything related
to these facets results in comprehensive but large quality models and extensive
measurements. In contrast, there are also many smaller, focused quality models
claiming to evaluate quality with few measures.
  We investigate if and to what extent it is possible to build a focused
quality model with similar evaluation results as a comprehensive quality model
but with far less measures needed to be collected and, hence, reduced effort.
We make quality evaluations with the comprehensive Quamoco base quality model
and build focused quality models based on the same set of measures and data
from over 2,000 open source systems. We analyse the ability of the focused
model to predict the results of the Quamoco model by comparing them with a
random predictor as a baseline. We calculate the standardised accuracy measure
SA and effect sizes.
  We found that for the Quamoco model and its 378 automatically collected
measures, we can build a focused model with only 10 measures but an accuracy of
61% and a medium to high effect size. We conclude that we can build focused
quality models to get an impression of a system's quality similar to
comprehensive models. However, when including manually collected measures, the
accuracy of the models stayed below 50%. Hence, manual measures seem to have a
high impact and should therefore not be ignored in a focused model.
