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A global rating scale is a scale used to summarize a patient's cognitive profile based on neuropsychological testing and/or clinical assessment. Two examples are the Global Deterioration Scale (GDS) and the Alzheimer Disease Assessment Scale (ADAS).

Research to evaluate effectiveness of a drug or other treatment is often measured in terms of changes in a global rating scale. For example, in a hypothetical experminent, a number of Alzheimer's patients are each randomly assigned to one of two groups. One group, the experimental group, is assigned to take a new experimental drug. The second, control group, is assigned to take a currently-available drug. At the start of the experiment, both groups have equivalent global ratings on a scale such as the GDS or ADAS. At the end of six months' time, both groups are again assessed in terms of the global rating scale. If the experimental group's scores have declined less than the control group's scores, this would suggest that the new drug may be more effective as a treatment for Alzheimer's disease.