Take "Worrying about your health", I think "worrying" here means "being anxious". So while normal health-conscious person cares about her/his health(eats well, sleeps well, takes necessary prescribed medications, etc), she/he isn't anxious about it. In contrast, depressed person may worry about her or his health without taking any actual steps to improve the situation.
Or take "Criticizing yourself or blaming yourself"(note second yourself, this question in kindle book is different, maybe I need to prepare correct pdf). If you spend your whole week under pressure of self-criticism, thinking about every mistake you made and every imperfection your work have, however small or large, then this is definitely 4. "Somewhat perfectionistic" is 1 in my book. 4 is "Extremely perfectionistic".
Or "Loss of interest in sex"? Why would an exteme loss of sex drive happen to a normal person?
Similarly for ‘worrying’ – does it mean ‘anxious’ or merely ‘concerned’? Taken to an extreme, I worry about my health when crossing the road. ‘Loss of interest in work or other activities’ also matches nearly everyone, given that people will lose interest in specific activities over time.
Certainly, such a questionnaire with a standardised interpretation and scale will be helpful, but you will need a professional to do such an assessment. To me, it looks as if it will over-diagnose people as unhappy/depressed.
Loss of sex drive is also something that can happen for a multitude of reasons – satisfaction found in work, for example, or other sources of stress.
Also, I am not saying that criticising yourself is not normal, I'm saying that spending all time criticising and blaming is not normal.
By the way, if your score actually more than 10, try other tools, Beck Depression Inventory for example. And try reading the book, you may find it useful even if you aren't clinically depressed. BTW, there is a chapter on perfectionism(which is quite common attitude in depressed individuals).
But I guess it is valid to ‘over-diagnose’ here, i.e. err on the side of caution, so it might even make sense to put in things that make sure anyone not absolutely fitting the standard ‘happy’ bill might be compelled to seek professional attention.
That assumes that a normal health-conscious person is.. healthy already. If you're overweight, or a heavy smoker, or maybe you have something wrong with you from headaches to cancer, surely there are plenty of reasons to worry about your health without it being a sign of depression?
If you're fat, and that makes you concerned, you're self conscious about being fat, and it's almost definitely going to hit your self esteem, if not cause you to be upset with yourself about eating/etc.