Computerized Dynamic Posturography (CDP) Sensory Test Scoring

Timothy C. Hain, MD • Page last modified: April 4, 2021 • Return to testing index

In these pages we are taking a deep dive into the scoring the Neurocom CDP sensory tests.

Composite Score.

The composite score is computed from sway elicited by 6 sensory conditions, as described here. These conditions are designed to be progressively more challenging, by combining 3 vision conditions (normal, no vision, distorted vision), and 2 support surface conditions (normal support surface, distorted support surface). These combinations are arranged so that for most individuals, the higher test # is more challenging.

The composite score, is the weighted average of scores for tests 3-6 combined with the average of tests 1 and 2. For example, if every test were done 3 times, there would be a total of 18 trials. The composite is the weighted average considering the average of test 1 to be one test, the average of test 2 to be one test, and then the other 12 tests. A total of 14 things to average. Thus, tests 1 and 2 are not weighted as heavily as 3-6, given that one administers a "full test", which includes 3 trials of 6 types of tests -- 18 overall. If a full test is not administered, the weighting is obviously idiosyncratic (not good).

CDP composite scores in dizzy patients in a broad group of dizzy patients.

The graph above shows mean composite scores as a boxplot from almost 2000 dizzy patients tested at Chicago Dizziness and Hearing. Graph made with "R".

Age is associated with a reduction in composite score. The large error bars show that the composite score is noisy when checked in "all comers" to a dizzy clinic. Of course, these measurements are not from "normal" subjects, but rather a mixture of many subjects with individual conditions. So some of the variability is likely due to subject composition, at least in part.

Pitfalls in the interpretation of the composite test

1. The operator is given discretion to do as few as one or as many as 3 repetitions of each test. The meaning of the "composite score" changes should one do less of one subtest or perhaps more of another.
2. The operator has the discretion to "warn" the patient of upcoming tests. This is an uncontrolled variable. It is particularly relevant for malingerer's who are attempting to "fail" the test.
3. Third, when the operator decides there is a fall, the trial is stopped and the score is set to 0. The point at which the operator decides to stop the test is uncontrolled.

 

References (for all CDP pages)