Mixing within and between age groups. The average number of encounters recorded in the paper diary between subjects and contacts in defined age categories is shown for a) all encounters and b) encounters involving physical contact. It should be noted that while averages are reported, the number of observations within each age group upon which these are based varies between 1 (70-79) and 22 (40-49). As can be seen, most contacts occur between individuals of the same age. Further, adults aged between 30-39 years mix with children under 10, presumably in the household. Similarly, 40-49 year olds have a large number of contacts with children and teenagers. Where only encounters involving some physical contact are considered (b), mixing between parents and children becomes more prominent.