Online thinking and memory tests for Alzheimer's disease have been called into question by a panel of experts.
Scientists led by Dr Julie Robillard, from the University of British Columbia, reviewed 16 online tests hosted on sites with up to nine million users.
They scored the tests on a reliability scale from one (very poor) to 10 (excellent). Twelve of the tests were rated as poor or very poor.
In addition every test had "poor" or "very poor" scores for ethical factors which included consent and conflicts of interest.
The results were presented on Tuesday at the Alzheimer's Association International Conference in Boston, US.
A spokesman from the Alzheimer's Society said: "It is understandable that people sometimes might want to turn to the internet for help if they are worried about their health. But what this research shows once more is that people need to be careful when considering online tests for Alzheimer's.
"Scientifically unsound tests could potentially give a false diagnosis while offering no emotional support, which could be devastating for the person carrying it out.
"If people are worried about their memory, or any cognitive problem, it is important that they go and see their GP."