The Standard & Poor 's 500 index declined by 4.39 , or 0.4 percent , to 998.88 , after losing 6.11 on Thursday .
The Standard & Poor 's 500 index declined 6.11 , or 0.6 per cent , to 1003.27 , having shed 19.67 in the previous session .
a sample that fully represents a population because each member of the population has an equal chance of being included.