More
Information on Using Gearing Factors
What is a gearing
factor? The gearing factor is simply the average number of Source Lines
of Code (SLOC) per function point in the completed project.
It is calculated by dividing the final code count for a completed
project by the final function point count. SLOC counts are logical,
not physical line counts.
What if the
language I am using is not in the table? If
you do not see the language you need in the table, you may
substitute a gearing factor from a comparable language. The
uncertainty range for the estimated gearing factor may be
increased to allow for any additional risk introduced by
using a substitute. You may also contact
QSM to see if revised information is available.
Should I use the average or the median? In a perfectly
symmetrical distribution of gearing factors, the average and the
median will be identical or very close. The average is obtained
by summing the gearing factors and then dividing by the number of
gearing factors included in that sum. Although its purpose is to
measure "central tendency", the average can be pulled up or down
by extreme data values (or outliers). The median, on the other
hand, is simply the data point that lies in the center of an ordered
list of gearing factors. One half of the data points will
lie above (and one half below) the median. When the data set
is skewed (biased either toward the high or low end by extreme data
values), the median may be a more accurate indicator of the central
tendency.
How
should I use the range? The range simply shows lowest
and highest gearing factors for each language. The range can
be used, with the average and median, to choose a "most likely"
gearing factor for estimation. The range can be useful as
a starting point for choosing an uncertainty range around your "most
likely" estimate of the gearing factor.

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