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Mean Absolute Deviation

Mean Absolute Deviation

The mean absolute deviation is also a measure of the variability of data in a sample. It is the absolute value of the average difference between the data values and the mean.
Let us consider a dataset containing the number of unsold cupcakes in five shops: 10, 15, 8, 7, and 10. Initially, calculate the sample mean. Then calculate the deviation, or the difference, between each data value and the mean. Next, the absolute values of these deviations are added and divided by the sample size to...

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Computerized Adaptive Testing System of Functional Assessment of Stroke

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Administration and scoring variance on the ADAS-Cog.

Donald J Connor¹, Marwan N Sabbagh

¹Cleo Roberts Center for Clinical Research, Sun Health Research Institute, Sun City, AZ 85351, USA. donald.connor@bannerhealth.com

Journal of Alzheimer'S Disease : JAD

|November 11, 2008

Summary

Alzheimer's Disease Assessment Scale - Cognitive (ADAS-Cog) variations reduce clinical trial reliability. Standardizing administration and scoring of this dementia assessment tool is crucial for accurate treatment effect measurement.

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Area of Science:

Neurology
Clinical Trials Methodology
Psychometrics

Background:

The Alzheimer's Disease Assessment Scale - Cognitive (ADAS-Cog) is a primary outcome measure in dementia clinical trials.
Variations in ADAS-Cog administration and scoring can compromise the reliability of trial results.
Rater variability, including turnover and drift, further impacts the instrument's consistency.

Purpose of the Study:

To investigate the extent of protocol variations in the ADAS-Cog among clinical raters.
To identify common ambiguities and problems in ADAS-Cog administration and scoring.
To emphasize the need for standardization to improve the reliability and sensitivity of the ADAS-Cog in clinical trials.

Main Methods:

A survey was distributed to 26 volunteer raters at a clinical trials meeting.
The survey collected data on variations in ADAS-Cog forms, administration procedures, and scoring rules.
Data analysis focused on identifying prevalent inconsistencies in the application of the ADAS-Cog.

Main Results:

Significant protocol variations were observed across different raters regarding ADAS-Cog forms.
Notable differences in administration procedures and scoring rules were reported.
These inconsistencies highlight potential sources of unreliability in ADAS-Cog assessments.

Conclusions:

The study confirms widespread variations in the application of the ADAS-Cog in clinical trials.
Standardizing the ADAS-Cog's administration and scoring is essential for enhancing its reliability.
Improved standardization will increase the sensitivity of the ADAS-Cog to detect treatment effects in dementia research.