Should objects be singular or plural in percentage statistics?

Question

I work in marketing, so I often see stats that reference smartphone penetration/usage.

Which of the following is correct? I've seen both.

65% frequently check items on their phone while in-store

65% frequently check items on their phones while in-store

What about:

Their confidence, camaraderie and try-it-once attitudes define every aspect of their lifestyle.

Their confidence, camaraderie and try-it-once attitudes define all aspects of their lifestyles

And:

Chinese male millennials depend heavily on their phones when shopping in-store.

Chinese male millennials depend heavily on their phone when shopping in-store.

Or:

65% say their phone is the most valuable tool when they’re in-store

65% say their phones are the most valuable tools when they’re in-store

Please help, this is so confusing! I, for the most part, get collective subject and plural/singular verb usage, but am often confused about the plurality and singularity of the object nouns.

Thanks in advance!

Answer 1

It should be singular ("phone") because each of the people (generally) have a single phone, and that's what you're talking about: the person's phone. When someone reads "65% frequently check items on their phone while in-store", they will imagine a generic person checking their phone in a store, not a survey's worth of people in thousands of different shops.

With "Male millennials have a try-it-once attitude.", it's the same rule: imagine you're talking about a single person. If they have one attitude you're interested in (eg their try-it-once attitude) then it's singular, if they each have multiple attitudes you're interested in then it's plural. For example, if you were talking about each male having several different attitudes (towards different things) you might say "Male millenials have different attitudes to their parents." for example.

So there's a sort of grouping effect: start with the individual, so it's the individual's attitude or the individual's phone, singular or plural as the situation requires for the single individual. Then when you talk about multiple individuals you pluralise individual (or "male millenial", or person, etc) but leave the thing they possess (the phone, attitude, etc) as is.

EDIT

I should add that while "Chinese male millennials depend heavily on their phones when shopping in-store." is technically not correct according to the rules I explain above, you will see this usage a lot, even in magazines etc: it's common to the point of being broadly acceptable. Many (perhaps most) people wouldn't take issue with it. But by being precise you help to avoid confusion.