Camerlink et al. (2018).

Population:	[Sow: Large White × Landrace] x [Boar: American Hampshire], Piglets, (UK).
Sample size:	Before weaning and before regrouping: 65 litters (683 piglets).After regrouping: 369 piglets (piglets below 12 kg, n = 11 piglets, were excluded). 10–13 piglets per group (average 12).
Intervention details:	Pre-weaning treatment groups: Treatment group was allocated based on parturition date. Group 1 control treatment (CON): n = 33 litters. Housing design: Littermate-only with sow in a farrowing pen until weaning.  Group 2 socialisation treatment (SOC): n = 32 litters. Socialisation housing design: Littermate-only with sow in a farrowing crate until day 14, then day 14 socialisation facilitated by an opening on the barrier between neighbouring farrowing crates. Socialisation group size: two litters pen (socialisation group size is the number of litters that interact with one another during lactation).
Study design:	Non-randomised controlled trial.
Outcome studied:	Weaning age: day 26. Socialisation length: 12 days. Regroup condition: Piglets were regrouped at 8 weeks of age. Selected at least 2 piglets from each of three to four litters in the same pre-weaning treatment group to form post-weaning groups. Balanced group composition between treatments. Post-weaning group size: 10–13 piglets per group (average 12), from three to four litters. SOC = 18 groups. SOC piglets were not regrouped with previously socialised piglets. CON = 14 groups. Behavioural indicators: Skin lesion (in the morning before regrouping, 24 hours after regrouping, 3 weeks after regrouping).
Main Findings (relevant to PICO question)	Behavioural indicators: Skin lesion: 24 hours after regrouping. Total skin lesions: SOC < CON (significant, P = 0.045).  Front: no significant difference. Middle: SOC < CON (significant, P = 0.047). Rear: SOC < CON (significant, P = 0.03). 3 weeks after regrouping (11 weeks of age). No significant difference between groups.
Limitations:	Only 369/683 (54%) piglets were regrouped and the selection criteria was not specified. Regrouping did not take place immediately at weaning. Skin lesion level before regrouping was not reported. Different group sizes after regrouping was not explained. The number of assessors for skin lesions was not specified. Exact number of piglets in each pre-weaning treatment group was not stated. The proportion of familiar piglet to unfamiliar piglet in a pen (familiarity ratio) after regrouping was not specified. Familiarity ratio is the number of familiar piglets (littermates or previously in same socialisation group) to the number of unfamiliar piglets (non-littermates and previously not in same socialisation group).