Falls can be avoided by installing grab bars in bathrooms and handrails on stairways; removing tripping hazards such as throw rugs; or installing window guards and safety gates at the top and bottom of stairs around young children. Playgrounds with shock-absorbing surfaces such as mulch or sand also prevent head injuries. Child abuse prevention is another tactic; programs exist to prevent shaken baby syndrome by educating about the dangers of shaking children. Gun safety, including keeping guns unloaded and locked, is another preventative measure. Studies on the effect of laws that aim to control access to guns in the United States have been insufficient to determine their effectiveness preventing number of deaths or injuries.