What's the difference between dementia and Alzheimer’s disease?
Dementia is an “umbrella” term that encompasses many types of cognitive deficits such as deficits in thinking, reasoning, memory, and attention.

Alzheimer’s is one disease that has symptoms of dementia.

Why can't one drive if one is at a cognitive level lower than 5.6 (Allen Theory)?
Performance at 5.6 includes the ability to understand the secondary effects of one’s actions. Regarding driving, this means one CLEARLY and QUICKLY (remember the speed of processing) understands that any movement of one's vehicle may impact another vehicle.

For example, if one needs to stop quickly because the vehicle in front of one has stopped, one must also be able to consider how stopping quickly may impact the person behind one. Merging onto a busy highway is another example of the need for 5.6 ability. One must consider how one's speed entering the highway will affect the other vehicles. If the person performing below 5.6 drives a familiar route to the grocery store, or to church, and nothing out of the ordinary occurs, then that person will travel safely.

We are all at risk when driving. However, the person without 5.6 abilities is at greater-than-average risk. In an unfamiliar situation or one that requires a quick response, the person without 5.6 abilities is at a greater risk of creating or suffering in an accident.