One must of course have access to the document (or documents) whose paternity is in dispute (they are called the Xs)—the originals would be optimal, but one must often make do with photocopies.

However, it is impossible to give a response with a 100% confidence without observing the original documents.

In almost all the cases (there are a few, very particular exceptions) one must also have a sizable amount of comparative documents (the Cs) certainly written by the person one suspects to have written the Xs.

Because of the graphical variability, the comparative documents should have been written in a situation as close as possible to that of the Xs, in order to minimise the accidental variability:

• Variability due to pathologies: in the case of degenerative pathologies, the documents should be written at the same stage of the illness.
• Variability due to substance (ab)use: alcohol, smoking, …, and drugs (especially the psychotropic ones) have relevant effects on handwriting.
• Variability due to time: the Cs should have been written within a small temporal distance from the Xs.
• Variability due to the writing instrument: the Cs should have been written with the same tools (pen, pencil, …) and in the same conditions (sitting, standing, in bed, …) as Xs.

It is also always important to have all the information that helps the graphologist take these possible variations into account: health state at the time of writing, drugs in use, …