I have a different view. When management changes its assets mix(having both the mentioned effects) shouldn't it change the company views on future in terms of returns and volatility due to change in assets position/structure during the analysis period?
As I mentioned above, different companies will categorise a change in asset mix differently within the analysis of surplus - so different views are fine! The original question was why the impact of a change in asset mix might be categorised as an economic variance rather than change in assumption, hence the response.
You are correct that a change in asset mix would change the volatilities that are modelled - but this can be considered to be different from changing the volatility
assumptions. A change in volatility
assumption could be changing your view from future equity market volatility being 20% to assuming that future equity market volatility will be 22%, say,
eg because you have performed better analysis. Changing asset mix is a management action which doesn't involve changing your
estimates of what the future might be (the average volatility modelled will be different due to having different asset class weightings, which are
known amounts, not due to making different
assumptions about the volatilities for each asset class) - hence it could be categorised separately from assumption changes.
Bear in mind also that the
expected investment return would not change as a result of a change in asset mix, assuming that we are talking about an analysis of surplus on a Solvency II basis. This is because Solvency II liabilities are determined on a risk-neutral market-consistent basis, so future
expected investment returns are set at the risk-free rate, irrespective of actual assets held.