Spend enough time discussing content marketing with marketers and those three little letters R-O-I will come up a lot! 

It's very difficult to measure the impact of a content strategy but the article I have referenced suggests a very sensible approach, (admittedly the words "extrapolation" and "formula" come up but it's a useful exercise)  in short you look at what you would have paid to get the same impact. 

You can apply a similar principle to the content you share on LinkedIn:

Count the total shares of your content and multiply by the average number of LinkedIn connections to work out your potential reach. 

Work out what you would pay for that many impressions via advertising or promoted content and you have a rough idea of the worth of your content.