QUICK FACTS
A Ph.D. candidate used PV-WAVE in her thesis and analysis of aging. The two studies contained in her thesis were set-up to examine how an aging person's postural control system maintains the structure of the musculoskeletal system in equilibrium with external forces. She used PV-WAVE to turn the loads of technical data she had collected into meaningful information.

THE PROBLEM
Most doctoral candidates agree that the success of their final thesis often depends on the effective management and analysis of a lot of data. When Clare Johnson, a Ph.D. candidate at The Pennsylvania State University, needed to turn reams of technical data into meaningful information, she knew insightful visualizations were possible only after powerful statistical analysis tools had been applied to the data. With that combination of functionality a prerequisite, Johnson turned to PV-WAVE, a data analysis software package developed by Visual Numerics.

Johnson, who has since earned a Ph.D. in Kinesiology, submitted a final thesis entitled, "Aging and Postural Control." Even though PV-WAVE eventually solved her problem, Johnson didn't begin the data analysis portion of her thesis using PV-WAVE. "I was using Matlab at first," she admits, "but I was having difficulty writing an adequate data analysis application, one that combined advanced visualization and statistical analysis. PV-WAVE was easier to tailor to my specific data analysis needs."

THE SOLUTION
Due to the sheer volume and complexity of the data gathered from Johnson’s study, she needed a data analysis and visualization product that could handle the "heavy lifting." As a result, she turned to PV-WAVE for fast, sophisticated and accurate results.

PV-WAVE allows users to visualize and manipulate complex or extremely large data sets to detect and display patterns, trends, anomalies, and other vital information. In addition, PV-WAVE includes hundreds of mathematical and statistical analysis routines from Visual Numerics' IMSL Numerical Libraries, as well as image processing, signal processing, mapping, and general data manipulation features.

To better understand Johnson's acute need for sophisticated data analysis software, one must first understand a little about her thesis.

Aging research is driven in large part by one indisputable fact -- the world's oldest populations are growing faster than any other age groups. Aging is an interesting phenomenon because individuals age at different rates and, even within a given individual, the various physiological systems age at different rates, rendering older adults more dissimilar as the years pass. New research methods continue to be discovered to help resolve this issue, and existing concepts and techniques from the physical sciences are now being applied to study the aging human body as a complex dynamical system.

The two studies contained in Johnson's thesis were set-up to examine how an aging person's postural control system maintains the complex, multi-degree-of-freedom structure of the musculoskeletal system in equilibrium with external forces while standing still and after taking a step.

The first study had two purposes: to extend the findings of past research and to apply the concept of approximate entropy (from the field of nonlinear dynamics) to determine whether an individual's center of pressure (COP) becomes less complex with age. The second study also had two purposes: to analyze the effect of step length and age on the time needed to reacquire stability following the execution of a step.

The findings put forth in Johnson's thesis provide evidence that dynamical stability is indeed a factor in postural research and suggest additional research into age-related changes of the human postural control system.

To carry out the second study outlined above, Johnson recruited 60 adults from both The Pennsylvania State University and the local community. The subjects were divided into four age groups: 20-29 years, 60-69 years, 70-79 years, and 80-89 years. There were 15 subjects in each age group. All of the subjects could walk independently and 90 percent indicated that they regularly participated in some form of physical activity.

A force plate from Advanced Mechanical Technology, Inc. was used to record the postural dynamics of each subject. The plate records three force components: the mediolateral force (Fx), the anterposterior force (Fy), and the vertical force (Fz); and three moment components: Mx, My, and Mz, which are the moments taken about the respective axes. The data was collected with a sample frequency of 50 Hertz (Hz) for a trial duration of 45 seconds. The force plate was connected to an IBM personal computer, which stored the data as it was recorded. Additionally, a video camera was placed orthogonal to the motion of the subject, positioned so that the field of view included the subject and the force plate.

The Institutional Review Board of The Pennsylvania State University granted approval of Johnson's testing protocol. Before the experiments began, each subject received a brief verbal explanation of the study and was given an opportunity to ask questions. After informed consent was obtained, the subject then self-reported date of birth and sex. In addition, the subjects filled out a ten-page questionnaire. The subject's height, weight, foot length, and preferred step length were also measured and recorded.

For the stance test, subjects removed their shoes and assumed a comfortable postural position with arms hanging at their sides. Each subject completed 15 trials of quietly standing on the force plate following completion of a predetermined step. The 15 trials required the subjects to reacquire a stable posture on the force plate under the following five conditions: after their preferred step length; after their preferred step length plus 5 percent; after their preferred step length plus 10 percent; after their preferred step length minus 5 percent; and after their preferred step length minus 10 percent. A block of three trials was performed in succession for each of the five conditions.

For the general postural test, subjects stood still and, once given the direction to proceed, stepped onto the force plate. The subject sought to maintain a stable position on the force plate for 45 seconds. At the end of the trial, an outline of the subject's feet was traced on graph paper that was affixed to the force plate. The distance from the starting line to the subject's heels was measured and recorded.

As necessitated by the complexity of Johnson's studies, the data analysis portion of her thesis was extensive. All the data was exported from the force plate, which resulted in 900 data files. Each file consisted of two columns of 2250 data points. Johnson developed several programs using PV-WAVE, which were used to determine the time to stability for each postural trial based on data acquired from the force plate.

RETURN ON INVESTMENT
"Making assumptions and drawing conclusions from the raw data would have been impossible. The sheer volume of information was overwhelming," Johnson said. "With PV-WAVE, I easily developed applications that allowed me to visualize the data. Once I could see trends in the data, the analysis and final results became clear. The final step in the data analysis process was utilizing Visual Numerics' IMSL statistical library, which is included in PV-WAVE Advantage, to verify the significance of the findings."

WORLD CLASS PRODUCTS, SERVICES, AND SUPPORT
Visual Numerics has provided technical software solutions for numerical analysis and visualization for over 30 years. The company's software products help users understand complex data from a variety of sources and build business-critical applications. Visual Numerics offers two product lines: the IMSL® Numerical Libraries for powerful mathematical and statistical analysis and the PV-WAVE® visual data analysis development environment. Visual Numerics also offers customized consulting services for applications that involve mathematical, statistical, or visual data analysis to meet today’s business analytical needs.