Robin McAlpine, who directs an organisation called Common Weal in Scotland, wrote a great blog for them yesterday under the above title.
What he quite effectively showed - using ONS and House of Commons data - was that Scotland is doing just fine as a UK region. The problem is that the whole of the UK suffers because London sucks the life, investment and income out of almost all its regions.
I won't do more than signpost the article here: I recommend reading it. And I endorse not only the analysis but also the suggestion that if Scotland was not a region but a country in its own right (which it is not at present) then its situation might be very different indeed.