Personally, I have found it helpful to hold a minimum of 25 or so stocks & limit any individual position to no more than 5 % of total portfolio value. (aaii.com)
Risk control based on risk per trade, risk control based on sector, risk control based on total portfolio. (trendfollowingmentor.com)
In fact, small changes in percentages will have little effect in total portfolio performance. (paulmerriman.com)