= Social group
In <animal behaviour>, a <social group> is a set of animals whose association and interactions are studied as a unit. Its operational definition specifies membership, the observation period and what counts as association. Sharing a location once need not establish persistent affiliation, and a group assembled for an experiment need not represent every naturally occurring grouping.
Group structure includes more than <social group size>. With $n$ members, there are $n(n-1)/2$ possible unordered pairs. A group of four therefore permits six distinct pairs, whereas a group of ten permits 45. These are possible relationships, not observations that every pair actually interacts. Recording which animals associate preserves information that a headcount discards.
Group membership also affects experimental interpretation. A study of <neophobia> compared 70 <Bengalese finches> in seven groups with 58 <white-rumped munias> in six groups. Feeding responses were recorded under familiar and novel-object conditions.<Effects of domestication on neophobia: A comparison between the domesticated Bengalese finch and its wild ancestor, the white-rumped munia by Kenta Suzuki and others>[Birds used in this study and novel-object procedure]{ref} The counts of birds and groups describe different levels of <replication>. If animals share a setting and influence one another, treating every bird as an independent replicate of a group-level treatment risks <pseudoreplication>. The appropriate <experimental unit> follows the treatment assignment and measurement design, rather than simply the largest available count.
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