  Quality requirements deal with how well a product should perform the intended
functionality, such as start-up time and learnability. Researchers argue they
are important and at the same time studies indicate there are deficiencies in
practice.
  Our goal is to review the state of evidence for quality requirements. We want
to understand the empirical research on quality requirements topics as well as
evaluations of quality requirements solutions.
  We used a hybrid method for our systematic literature review. We defined a
start set based on two literature reviews combined with a keyword-based search
from selected publication venues. We snowballed based on the start set.
  We screened 530 papers and included 84 papers in our review. Case study
method is the most common (43), followed by surveys (15) and tests (13). We
found no replication studies. The two most commonly studied themes are 1)
Differentiating characteristics of quality requirements compared to other types
of requirements, 2) the importance and prevalence of quality requirements.
Quality models, QUPER, and the NFR method are evaluated in several studies,
with positive indications. Goal modeling is the only modeling approach
evaluated. However, all studies are small scale and long-term costs and impact
are not studied.
  We conclude that more research is needed as empirical research on quality
requirements is not increasing at the same rate as software engineering
research in general. We see a gap between research and practice. The solutions
proposed are usually evaluated in an academic context and surveys on quality
requirements in industry indicate unsystematic handling of quality
requirements.
