[pandaman]

People living their whole life in apartments do not create nearly as much nuisance as people who moved into apartments from detached houses, where they grew up. They don't wear hard-soled shoes inside, they don't drop stuff on the floor, they don't blast music and don't even own 1500W subwoofers, or weight racks, or treadmills.

For some reason people believe that a little baby is the most noise possible and it's often used in such discussions as an evidence of complete sound-proofing of their dwellings. While people do instinctively get agitated from a child's screams the power of these screams is very low. This is why parents get baby monitors as the screams don't propagate well even between floors in a single-family house. Even adults, unless trained, can't scream nearly as loud as a 200W Bluetooth speaker. Get your neighbor upstairs to drop an empty barbell bar and see how you won't notice it. And in the US your neighbor can be dropping a 300 pounds barbell while having a party with people dancing with accompaniment of 2.5kW sound system, at 2:30 am.

[EVa5I7bHFq9mnYK]

Rented six apartments in the US. Only once had a noise problem, solved by an email to the leasing office. Though admittedly they were all in the "nice" neighborhoods.

[pandaman]

With the 46.8M multi-family units in the US, that bing shows, your sampling of six is not very significant.

[EVa5I7bHFq9mnYK]

If the percentage of noisy apartments were 90%, the probability of me randomly landing in 6 quiet apartments out of 6 would be 0.1^6, or one in a million. If the percentage of noisy apartments was 10%, that probability would be 0.9^6 = 0.53. So, given my experience, the latter case is 0.53 / 0.000001 = 530,000 times more probable.

[pandaman]

"conditional probability" is the concept you might find enlightening.

[EVa5I7bHFq9mnYK]

You may start with "How Many Jelly Beans?: A Giant Book of Giant Numbers" by Andrea Menotti.