SuttaCentral
Some overestimate their attainments. Others don’t want to reveal out of fear of being ostracised. The ordained don’t want to reveal it, due to vinaya blocks. It’s creates confusion for the jhana attainers of the future.
Answer? Is limiting it to teacher student situations adequate, as many will miss out?
Its further complicated by different teachers having different interpretations of the jhanic states, and for example what intensity of piti and sukha are “required”.
Quite.
However I find IMO two groups…
The first group hold questions about different definitions about jhana from various teachers of jhana. There’s fluidity…
The second group have more fixed definition of jhana. They might challenge others. I think there’s a chance, that people who practice, and are in this category may have actually experienced it.
And a third group who have had significant experiences but are not sure whether they count as jhana, since it depends whose definition one favours.
Whippet I would clarify my groups ~ group 1: doubts 2. certainty. [This certainty may be based on actual experiences of jhana or rarely delusion about having attained jhana]. I think either group could have jhana attainments but I think it far more likely that group 2 has them as not many would insist if they hadn’t achieved them and weren’t therefore certain, if that makes sense, and I’m assuming people are being honest.
The problem is that there is no consensus on what jhana is. And of course there is an inherent subjectivity about meditative experiences.
I think the reason for doubt is that the practitioners haven’t experienced jhana, because if they did they would be free from vacillation.
Equally a person who has seen anatta wouldn’t have doubt (about anatta).
I just think it’s all horribly subjective. There is no objective means of measuring mental states or insights.
A teacher at a retreat I attended told the story of her jhanic experience - she thought she had attained enlightenment, but her teacher told her that it was “just” a jhana state. She was fortunate to have a qualified teacher available at the moment to correct her misinterpretation. This is just one anecdote, but I think your group 2 can easily contain a lot of people who have experienced some kind of state of altered consciousness, but misinterpret it, due to the lack of guidance from such a qualified teacher.
But different teachers define jhana differently. It’s not like there is some objective standard for these experiences.
Notice that I use the phrase “qualified teacher”. There are a lot of unqualified teachers running around, IMHO. For my own evaluation of teachers, I look for those who
There are more groups, but I 
this distinction.
We could add to the list:
The silent ones who have experienced jhana but wisely say nothing about it.
And also, their opposite, the ones who say too much about jhana but have never experienced it.
Plus, I would add those to be wary of:
People whose “jhana” definition is unorthodox, idiosyncratic, self-verified, not recognised by teachers of jhana as jhana, does not fit with the suttas, the tradition, or with the lineage of meditation teachers practicing jhana.
Those who say jhana is simple and easy. Who devalue and diminish jhana, by taking something supramundane and making it mundane, taking something extraordinary and making it ordinary; rendering it meaningless by defining it in a way that makes it easier to “attain”, so that you can be practicing jhana whilst at the bus stop, or thinking about your groceries whilst doing jhana… Um. 
No.
And those who make claims out of conceitedness,
arrogantly overestimating their experience to puff up their egos, feel that they are somehow ‘special’ and that they are superior to others. If they had actually experienced jhana, it should have dissolved rather than solidified their sense of self!
These “experts” can greatly mislead others.
Watch out!!
Sure, but there is no objective standard here for “qualified” either. It comes down to personal faith in this or that teacher or interpretation, as with other aspects of Buddhist teaching and practice.
Anyone can admit their limitations, especially those who have limitations regarding a particular aspect of practice. But it nevertheless helps…
Referring to suttas are essential. But many views can be justified this way too.
When I say group 1, I think 95% may not have attained jhana and in group 2 (the more certain ones) 95% may have attained jhana, and the others have some degree of samadhi at least.
You can measure time with a clock. You can’t measure a meditative state, you can only attempt a subjective description - and then compare it to a written text, which is itself based on subjective translation and interpretation. Or you can compare it to descriptions by “qualified teachers”, but those are varied and inconsistent. And are we talking about sutta jhana or commentarial jhana? There are degrees of piti for example, but what degree is sufficient to call it jhana? And so on.
I agree that jhana isn’t easy. What I’m pointing to is the lack of consensus on how difficult it is, and the lack of an objective standard for what exactly qualifies as jhana.
I don’t disagree with your statement regarding the lack of objective standards, but I don’t understand why it is so important to you. “Objective” as you use it seems to be synonymous, or nearly so, with “scientific” and “measurable”. While I believe science should not be ignored, I don’t think science has developed to the point where it can offer us much that is specific and reliable regarding even mundane psychological states, let alone the supramundane. I’m not sure science will ever progress to that point, because science is led (now as always) by profit-making motives - and there is not much profit to be made in measuring jhana.
To clarify, this is not intended to be an exhaustive list of teacher qualifications, which is not the topic of this thread. I only listed some things I felt were relevant to the thread.
I’d be content with a commonly agreed standard, but even that is lacking. It depends who you talk to!