Studies have shown that the diffusion rate for many new technologies is speeding up. The figure, "Household Penetration of Selected Communications Technologies" (left), illustrates U.S. household penetration rates of selected communications technologies, measured as a percentage of all households. The slope of the curve becomes steeper with each successive innovation indicating a more rapid diffusion rate. For example, it took decades for the telephone to achieve 50 percent penetration rates beginning in around 1900, but it took less than five years for cellphones to achieve the same penetration rates. In order to explain the increasing pace of adoption, some have pointed to supply-side issues such as reduced barriers to entry and lower costs of innovation, while others have argued that consumers drive adoption rates because they place a high value on the convenience of new innovations.