### Instruction:

Extract the cause and effect entities from the following sentence:
The statistical study of structures in a large volume of the Universe requires a survey of a large fraction of the extragalactic sky

### Assistant:

VARIABLE: The statistical study of structures
KEYWORD: requires
EFFECT_1: a survey of a large fraction of the extragalactic sky
CONDITION: of a large fraction of the extragalactic sky
CAUSE_1: The statistical study of structures in a large volume of the Universe

