explain Peter Singer's impartial spectator

Singer’s preference utilitarianism as laid out in his book practical ethics, asserts that when thinking ethically one should take the view of the ‘impartial observer’. By this he means that your own interests cannot take precedence over anyone else’s interest just because they belong to you. One has to take into account everyone who is effected when making an ethical decision, and ‘weigh up all these interests and adopt a course of action which has the best consequences on balance, for all affected’ (page 12). It does not matter who you are, everyone under this theory is equally weighted. When choosing whether to help one person or another, you cannot base your decision on whether one of the people is related to you in some way. Rather base the decision on what would maximise the overall preferences of all involved.