The Heaping Effect in the Survey Data on the Number of Friends

The number of acquaintances is relevant for modeling social networks. Here we consider the data on the declared number of friends, as collected in 2000, 2007 and 2015 from Polish respondents above the age of 50. We demonstrate that the answers on the number of friends show sharp maxima at 10, 15, 20 and sometimes 30, which accompany a broader peak between 0 and 8. These results do not change qualitatively with sex and age of the respondents. The effect, known as data heaping, can be detected as a deviation from the Benford law.