A study done by Dr. Jane Morton at Stanford University showed that mothers that used a Hands on Pumping technique along with hand expression increased milk Mean Daily Volumes (MDV) by 48%. This study shows that even very high quality pumps by themselves do not maximize a mothers milk production. A breastpump leaves a residual volume that only external compression seems to remove. Hand expression will stimulate the nipple/breast and massage will help to empty the breast more completely. This also removes the rich hindmilk fr the baby. Simplicity is a product that facilitates this process by holding the breastpump horns so a mothers hands are free. You can read the full article here.
Study Shows Hands on Pumping Increases Milk Volumes