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.