All but one of my questions since September have gone unanswered. I am not complaining, of course: there's no reason why my questions should be answered. It's just that it seems to me that the style and type of questions hasn't strongly changed with respect to older questions. Thus I wonder, is there a general trend on CV, where the ratio of unanswered to answered questions is growing? Or am I wrong and my newer questions are less interesting and/or well written than the older ones? Can I do something to improve the likelihood of an answer? Other than putting bounties on each question, of course :)
The proportion of unanswered questions is indeed slowly growing because (among other things):
the number of people answering questions is growing more slowly than the number of people asking questions.
the proportion of very poor questions is increasing rapidly, sapping the time-resources of the very people who tend to answer questions into dealing with clarifying or closing questions.
I doubt this relatively slow process is the cause of a sudden drop in answers for you, however.
Part of it may be a matter of luck but you can certainly improve your chances of an answer by working on your questions. Several questions already on site here deal with such issues.
Looking at your recent questions, at least some of your questions seem unlikely to be of broad interest (for all they are sure to be useful to you personally); that will reduce interest in answering them; it's fine to ask but they won't necessarily be priorities. You can consider ways to make some of those questions more generally useful, which may help make them interesting to answerers.
You can also make it easier for people to answer some of your questions.
For example, the most recent one asking about references on probability links to three references but mentions neither the authors nor the year of publication. Since many books on probability have similar or even identical titles, the titles alone don't really identify them. So when I see a question like that, I have to ponder whether I have time to start loading page after page on Amazon just to find out what books you're even talking about.
I'm kind of busy (and then when I am here there's a lot of tasks to take care of besides answering questions) and even without that, there's more questions a day than I can even read, let alone give a worthwhile answer to, so if my connection is slow enough to make it take a few seconds each page, it's likely to be "Sorry, next question". I imagine at least some other answerers may be in a similar position.
Clicking through now, I only know one of those books. So even if I did decide I have time to click through to find the books, I would disqualify myself from offering a choice; again it would be a case of "Sorry, next question". [A rephrase of the question may make it more likely to draw at least partial answers.]
Lastly, a number of of your questions are outside my area of knowledge, or are just about within it but so specific I doubt I have enough specialized knowledge to give a useful answer. This, too, may be the case for several other potential answerers.
I now have some experience with CV and other SE venues. I think CV is more challenging than others because questions are more technical and scientific, and also because subspecialization is the rule in statistics.
My recommendations to improve your likelihood of getting a correct answer are the following:
try to put your question in a comprehensible fashion, avoiding acronyms and jargon;
use correct tags (and as many as appropriate) as this is likely to boost interest to those subscribing for particular topics;
expand your question so that it reads as an intelligent and provocative piece on this topic;
try to put the question into context, for instance by providing a sample database and code for a popular package (e.g. R); this will attract those more interested in specific packages and also help them give you a practical solution;
return often to improve it by editing and boosting its content;
if you find a solution yourself, then post an answer.
This is more a trick than an advice, but I feel that submitting a question when most users are online (e.g. when it is afternoon in North America) will increase your visibility.
In addition, I think as a community we need to upvote more the answers than the questions.