Well, do we know the sample size? 10s, 100s, or 1000s? And were there equal numbers of registered to non-registered engineers?


There are many more non-registered compared to registered engineers in employment. So what about age range? What if they questioned say 10 senior registered engineers in the 40-50 age range, and 100 or more junior non-registered engineers in the 20-35 age range? 


Some organisations provide london weighting pay on top of basic salaries.  All of these factors could have an added effect to skew the results in favour of registered engineers, who just might all happen to be based in London. 


In my experience, I have observed that highly skilled, but fixed job roles, tends to result in lower salaries compared to earnings of those who have multiple roles or responsibilities. That's another factor that might explain, why one engineer is paid more than another.

Well, do we know the sample size? 10s, 100s, or 1000s? And were there equal numbers of registered to non-registered engineers?


There are many more non-registered compared to registered engineers in employment. So what about age range? What if they questioned say 10 senior registered engineers in the 40-50 age range, and 100 or more junior non-registered engineers in the 20-35 age range? 


Some organisations provide london weighting pay on top of basic salaries.  All of these factors could have an added effect to skew the results in favour of registered engineers, who just might all happen to be based in London. 


In my experience, I have observed that highly skilled, but fixed job roles, tends to result in lower salaries compared to earnings of those who have multiple roles or responsibilities. That's another factor that might explain, why one engineer is paid more than another.