Dunbar’s Number

Calling Dunbar’s Numbers
Pádraig MacCarron, Kimmo Kaski, Robin Dunbar
4 Aug 2016

The social brain hypothesis predicts that humans have an average of about 150 relationships at any given time.
Within this 150, there are layers of friends of an ego, where the number of friends in a layer increases as the emotional closeness decreases.

Individuals do not give equal weight to each relationship and evidence from the social brain hypothesis suggests that ego networks are structured into a sequence of layers with the size of each layer increasing as emotional closeness decreases (Dunbar 1998, Hill and Dunbar 2003).
The mean number of friends in each has been found to be around 5, 15, 50 and 150 in the cumulative layers (i.e. on average 10 people in the second layer to make a total of 15) (Zhou et al. 2005, Hamilton et al. 2007).

A lifestyle intervention in preschool children (Ballabeina)

Influence of a lifestyle intervention in preschool children on physiological and psychological parameters (Ballabeina): study design of a cluster randomized controlled trial.
BMC Public Health. 2009 Mar 31;9:94.
Niederer I1, Kriemler S, Zahner L, Bürgi F, Ebenegger V, Hartmann T, Meyer U, Schindler C, Nydegger A, Marques-Vidal P, Puder JJ.

Childhood obesity and physical inactivity are increasing dramatically worldwide.
Children of low socioeconomic status and/or children of migrant background are especially at risk.
In general, the overall effectiveness of school-based programs on health-related outcomes has been disappointing.
A special gap exists for younger children and in high risk groups.

This paper describes the rationale, design, curriculum, and evaluation of a multicenter preschool randomized intervention study conducted in areas with a high migrant population in two out of 26 Swiss cantons. Twenty preschool classes in the German (canton St. Gallen) and another 20 in the French (canton Vaud) part of Switzerland were separately selected and randomized to an intervention and a control arm by the use of opaque envelopes.
The multidisciplinary lifestyle intervention aimed to increase physical activity and sleep duration, to reinforce healthy nutrition and eating behavior, and to reduce media use.
According to the ecological model, it included children, their parents and the teachers.
The regular teachers performed the majority of the intervention and were supported by a local health promoter. The intervention included physical activity lessons, adaptation of the built infrastructure; promotion of regional extracurricular physical activity; playful lessons about nutrition, media use and sleep, funny homework cards and information materials for teachers and parents. It lasted one school year. Baseline and post-intervention evaluations were performed in both arms. Primary outcome measures included BMI and aerobic fitness (20 m shuttle run test).
Secondary outcomes included total (skinfolds, bioelectrical impedance) and central (waist circumference) body fat, motor abilities (obstacle course, static and dynamic balance), physical activity and sleep duration (accelerometry and questionnaires), nutritional behavior and food intake, media use, quality of life and signs of hyperactivity (questionnaires), attention and spatial working memory ability (two validated tests). Researchers were blinded to group allocation.

The purpose of this paper is to outline the design of a school-based multicenter cluster randomized, controlled trial aiming to reduce body mass index and to increase aerobic fitness in preschool children in culturally different parts of Switzerland with a high migrant population.

The CON group continued to follow their usual school curriculum which included one 45 min physical education lesson taught by the classroom teachers and one 45 min rhythmic lesson (given by a rhythmic specialist)

… PA lessons were given four times a week including 40 min lessons and 5 min cool down.

…Results of the intervention will be available in 2010.

Urie Bronfenbrenner