\section*{Appendix: Data Used in This Study}
\label{sect:data-used-in-this-study}

All the data used in this study is 
available either at \protect\url{http://promisedata.org/data} or through the
authors.
As shown in \fig{datasets}, our data includes:
\bi
\item The desharnais and albrecht data sets;
\item
 sdr, which is data from projects of various software companies in Turkey.
sdr is collected by Softlab, the  Bogazici University Software Engineering Research 
Laboratory repository~\cite{Bakir2009};
\item
And the standard COCOMO data sets (cocomo*, nasa*). 
\ei

Note that some of these data sets (nasa93\_center\_1, nasa93\_center\_2, nasa93\_center\_5)
come from different development centers around the United States and some datasets (cocomo81e, cocomo81o) represent different kinds of projects:
\bi
\item The cocomo81e  ``embedded projects''
are those developed within tight constraints (hardware, software, operational, ...);
\item
The cocomo81o ``organic projects'' come from
small teams with good experience working with less than rigid requirements.
\ei

Note also in \fig{datasets}, the skewness of our effort values (up to 6.06):
Our datasets are extremely heterogeneous with as much as 60-fold
variation.  
There is also some divergence in the features used to describe our data:
\bi
\item 
While our data includes some effort value (measured in terms of months or hours),
no other feature is shared by all data sets.
\item
The cocomo* and nasa* data sets use the features defined by Boehm~\cite{Boehm1981}; e.g.
analyst capability, required software reliability, memory constraints, and use of software tools.
\item
The other data sets use a wide variety of features including, number of entities in the data model, number of basic logical transactions, query count and number of distinct business units serviced.
\ei

