NAME
   Medical::Growth - Basic tools for growth-dependent norms

SYNOPSIS
     use Medical::Growth;
     my(@systems) = Medical::Growth->available_systems;
     my $meas = Medical::Growth->measure_class_for(system => My::System,...)
     my $z_score = $meas->value_to_z($value, @criteria);

DESCRIPTION
   Medical::Growth is designed as a common resource for implementing
   systems of growth-dependent norms. It provides a set of basic tools for
   operating on normally distributed data, as well as a common entry point
   for users of Medical::Growth-compatible systems.

   If you're interested in using a Medical::Growth-compatible measurement
   system, read on. If you're interested in building a measurement system,
   you may also want to see Medical::Growth::Base, which contains some
   tools to facilitate the process.

 USING MEASUREMENT SYSTEMS
   In conceptual terms, a collection of methods that allows you to compare
   a measured value to a set of norms is called a measurement system. For
   instance, the models for anthropometric values based on the NHANES 2000
   survey, from which growth charts in common use in pediatrics were
   created, is a measurement system.

   In pragmatic terms, a measurement system is a collection of classes that
   present a common set of ways to compare a measurement to norms. Each
   specific comparison is done via a measurement class, which provides an
   interface for a specific set of norms. To continue the NHANES 2000
   example, a measurement class would correspond to a single growth chart,
   that is, the collection of norms to which you would compare a specific
   value. Thus, weight for age in boys 2-20 years old would be a
   measurement class, while length for age in girls under 3 would be a
   separate measurement class. In some cases, such as these, a measurement
   class will need to know only one value (here, age) in addition to the
   measurement to return the normalized score. In others, it may need
   several additional pieces of information. Where to draw the boundary
   between different measurement classes and a single measurement class
   using multiple indices may be different for different measurement
   systems, and reflects the best interface design for common use.

   Medical::Growth provides two methods to simplify interactions with
   measurement systems:

 METHODS
   available_systems
       Returns a list of the names of measurement systems installed in the
       Medical::Growth hierarchy.

   measure_class_for(*%criteria*)
       Locate a measurement class that performs the function specified by
       *%criteria*, and return a handle that allows you to call methods
       from the measurement class. This is provided as a common entry point
       to make finding measurement classes easier. Although nothing stops
       you from hard-coding the name of the measurement class directly,
       finding it via "measurement_class_for" may help keep your code more
       readable, and may let you take advantage of shortcuts provided by
       the measurement system.

       Most of the work is done by the "measurement_class_for" method in
       each measurement system, since it requires detailed knowledge of how
       a particular measurement system is implemented. The Medical::Growth
       version of this method uses the value in *%criteria* associated with
       the key "system" to identify the measurement system you want. This
       value can be the full name of a measurement system's top-level
       class, as returned by available_systems, or it may be an abbreviated
       name without the leading "Medical::Growth::". The top-level class
       for the measurement system is loaded, if necessary, and its
       "measurement_class_for" method is called, with *%criteria* as
       arguments. It is up to the measurement system's
       "measurement_class_for" to interpret the rest of *%criteria* and
       return the appropriate handle.

       If the "system" element is missing from *%criteria* or the class
       cannot be loaded, an exception is thrown.

 EXPORT
   None.

DIAGNOSTICS
   Any message produced by an included package.

   No measure_class_for() method found (F)
       Medical::Growth::measure_class_for found a measurement system
       matching the "system" specified and loaded its top-level module, but
       that module didn't provide a system-specific "measure_class_for" to
       pick a measurement class.

BUGS AND CAVEATS
   Are there, for certain, but have yet to be cataloged.

VERSION
   version 1.00

AUTHOR
   Charles Bailey <[email protected]>

COPYRIGHT AND LICENSE
   Copyright 2014 Charles Bailey.

   This software may be used under the terms of the Artistic License or the
   GNU General Public License, as the user prefers.

ACKNOWLEDGMENT
   The code incorporated into this package was originally written with
   United States federal funding as part of research work done by the
   author at the Children's Hospital of Philadelphia.

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