Knowing the area of involvement helps us understand a persons symptoms like pain.
A problem localised to a point is clearly different from problem covering an area.
Pain can spread into another region. Chronic pain often affects large portions of the body. How do we measure these differences?
The extent of involvement can be assessed by dividing the body into sections.
The number of sections that the drawn region extends into is the "extent" or area affected.
Most research has used drawings divided into sections ranging from 6 to 15,000 (Ljunggren 1983; Donelson et al. 1991; Toomey et al. 1983; Love, Leboeuf & Crisp 1989; Margolis et al. 1986; Gatchel et al. 1986; North et al. 1992). Most analyses were done by hand.
Bryner (1994) demonstrated that pain extent is systematically overestimated by up to 600% (Figure 5).
This overestimation can be minimised by using the smallest unit of the computer display – the pixel.
Screen resolution has increased substantially over the last 20 years from 600X480 (288k pixels) to more than 1280X960 (1,229K pixels) an increase of 420%.
As of 2009, the size of the image is still affected by many factors.
These can include such issues as: the screen resolution on the computer used to deliver the pain drawing, the tool used to complete the computerised drawing (mouse, touch screen, pointer with touch screen).
A lower screen resolution means that the technology is available to more potential users at lower cost.
A large image that displays at a moderate size on a hi-resolution screen will extend well outside the edges of the screen of a lower resolution screen.