There were actually two surveys conducted. The first had a sample of 1,843 men and women aged from their teens to 49 years old, and the second involved a subset of 335 people from the original sample (I think – it is not too clear) who had identified themselves as otaku in Q1.
Although the demographics are confusing, there does seem to be an indication that the eldest child is an otaku. There is perhaps a reason involving Japanese family structure, but what that might be I have no idea! I welcome any wild speculation from my readers!
These holy grounds are the real life locations represented in various anime and manga; for instance, here is their entry for the hot springs and hotel in Sprited Away/Sen to Chihiro no Kamikakushi.
Q1: Do you consider yourself an otaku? (Sample size=1,843)
Yes (to SQs (sort of)) 37.4% No 62.6%
Q1SQ1: What position are you in the order of your siblings? (Sample size=335)
Only child 16.4% Oldest brother, oldest sister 59.1% Second brother, second sister 14.3% Third brother, third sister 3.3% Youngest overall 6.3% Other 0.6%
Q1SQ2: Who of the following have found out you are an otaku? (Sample size=335, multiple answer)
Friends 67.2% Parents 62.1% Brothers, sisters 51.0% Acquaintances 32.2% Work colleagues 22.1% Other relatives 20.3% Other 4.8% No-one 9.6%
Q2: What image do you have of an otaku? (Sample size=1,843, multiple answer)
Get lost in their favourite hobby 61.9% Love anime 50.4% Know a lot about a single subject 47.9% Have their own little world 46.8% Akihabara 45.6% Determined 41.5% Love manga 38.8% Love computer games 37.8% Wear a rucksack 23.5% Female otaku numbers increasing 18.9% Wear a bandana 14.5% Wear check shirts 13.9% Carry paper bags 13.7% Recently stylish 6.0% Trousers with lots of pockets 4.8% Other 2.0% Nothing in particular 6.2%