The economic data that drives so much political debate is becoming increasingly less reliable in the digital era. That’s because new technology makes it hard to compare the 21st-century economy to anything that came before it.

How, for example, do you compare the living standards of a middle-income American in the 1970s with a middle-income American today? The 1970s version had no cellphone, no Internet, no digital camera and was limited to watching one of three television networks. That sounds primitive by today’s standards.