devaluation of knowledge 
I read somewhere the following "theorem":

> In Information Technology related  jobs 60% of learned knowledge is not useful after 1.5 half year

I'm not sure if I remember numbers correctly (but I think they are close to original) and the author of this theorem. Also I'm not sure if this was about general IT knowledge or domain knowledge. I was googling a lot for it, but unfortunately I can't find it.

So my firs question is: where can I find the correct version of this statement?

I have also same open questions related this subject.

I talked about this with my colleagues from university and one of them said that this is theorem about stupid person that can't find out what is important to learn. I disagree with him. He is good mobile applications developer. But would be he so good after spending years on a desert island (of course with out his Android based phone ;) or other Internet enabled device)?
However I think he has right about one important thing - devaluation comes faster or slower depand on knowledge type. And this is my last question: What programming ralated skils doesn't lose value over time?

Some interesting links:

 - http://www.slideshare.net/Al.Simard/knowledge-management-value-chains
 - http://www.slideshare.net/BillHall/time-value-of-knowledge-timebased-frameworks-for-valuing-knowledge
 - http://c2.com/cgi/wiki?WhyIsDomainKnowledgeNotValued - "DomainKnowledge should be maintained the same way a codebase is maintained"
 -http://www.tinbergen.nl/cost/cost/gustavsson.pdf this studies show that 5% of  skills are lost after one year of unemployment.
devaluation of knowledge 
===

I read somewhere the following "theorem":

> In Information Technology related  jobs 60% of learned knowledge is not useful after 1.5 half year

I'm not sure if I remember numbers correctly (but I think they are close to original) and the author of this theorem. Also I'm not sure if this was about general IT knowledge or domain knowledge. I was googling a lot for it, but unfortunately I can't find it.

So my firs question is: where can I find the correct version of this statement?

I have also same open questions related this subject.

I talked about this with my colleagues from university and one of them said that this is theorem about stupid person that can't find out what is important to learn. I disagree with him. He is good mobile applications developer. But would be he so good after spending years on a desert island (of course with out his Android based phone ;) or other Internet enabled device)?
However I think he has right about one important thing - devaluation comes faster or slower depand on knowledge type. And this is my last question: What programming ralated skils doesn't lose value over time?

Some interesting links:

 - http://www.slideshare.net/Al.Simard/knowledge-management-value-chains
 - http://www.slideshare.net/BillHall/time-value-of-knowledge-timebased-frameworks-for-valuing-knowledge
 - http://c2.com/cgi/wiki?WhyIsDomainKnowledgeNotValued - "DomainKnowledge should be maintained the same way a codebase is maintained"
 -http://www.tinbergen.nl/cost/cost/gustavsson.pdf this studies show that 5% of  skills are lost after one year of unemployment.