The answer is that it is hard to tell. I did some research because I wanted to better quantify the number of visitors that I have had at this blog in its six-year lifetime, and what I learned is that you can make a guess, but due to the nature of the Internet you never can get to an exact number.
For example, in WordPress it shows that one of my articles had 30 views. However in LinkedIn, it shows that 130 people read it. If I look in Google Analytics, it says 50 people viewed it. If I use a different WordPress hit counter, it gives me a different number. If I look at the shares in the social networks from the plugin that automatically uploads it to different networks it says 500 shares for the day. Which number am I supposed to believe?
I understand the difference between page views, hits and unique visitors. The numbers above are unique visitors. I don’t care how many hits/views I get because I can’t quantify that into anything meaningful. What would be helpful is if all of the sources that cache an article could report back to the original source and inform it how many unique visitors read it. Sometimes as authors in WordPress we might feel sad when we would only have 30 people read it, but given how complex the Internet is, it is not correct that only 30 people read it. Of course it would be difficult to measure how often it might be emailed, captured to a pdf or something like that, but getting closer to a realistic number.
Some websites say that you can get a better number by cookie tracking, but lots of people don’t have their cookies turned on. In addition, I don’t like invading people’s privacy with tracking tools, so philosophically I am opposed to tracking people. If people want to share information that is one thing, but I don’t believe that people want to be tracked.