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.
| Score | Formula | Compared | Apparent | Intent |
|---|---|---|---|---|
| Composite | 1+2+3*(3+4+5+6)/3 | weighted sum | Weighted average | Average |
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
- 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.
- 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.
- 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.