I would like to first comment that there is one thing that you keep repetitively bringing up the same point, which I already eliminated. In this reply, I will highlight my points with bold font so that you can perhaps see what I was trying to say.
(*) This study has a roughly three major groups: Asian, African, European. Rest of the sample population has American, Oceanian, etc. All the minor breakdowns are noted for peer review which has nothing to do with what paper is trying to test.(*) Other studies I cited are more detail focused. Say only on japanese, and chinese. therefore, do not suffer the similar problemsQUOTE(fcharton @ Oct 23 2006, 03:34 PM) [snapback]4856813[/snapback]
Thanks for your patience, here is what I understand (trying to summarise in case other neophytes, like me, are interested in the subject).
Well, I appreciate that you recognize the importance of explaining words in simple words.
QUOTE(fcharton @ Oct 23 2006, 03:34 PM) [snapback]4856813[/snapback]
We are looking at the sequence of genes, which are present on the Y chromosome of men. The idea is that one’s version of this chromosome is inherited from one’s father, from which it is a “perfect copy”, because these genes are copied at birth, and very rarely change over time. As such, all male descendents of the same ancestors should have the same Y chromosome, unless a mutation of the gene has occurred, which is very unlikely over short periods of time.
As such, when looking at the genetic patrimony of two individual we can, by focusing on the differences between their Y chromosomes, get an idea of the closeness between them (how far back is their common ancestor).
ok.
QUOTE(fcharton @ Oct 23 2006, 03:34 PM) [snapback]4856813[/snapback]
Better still, and I think this is what you call phylogeny, by looking at a specific differences (ie past mutations), you can draw some kind of “family tree” of groups of people, by classifying them according to the presence in their patrimony of certain specific differences (mutations). I believe this is what is called a “marker”. The idea behind phylogeny is that mutations are so rare, and we have so many genes, that the possibility of the same “marker” happening twice in an unrelated manner is extremely low.
I don't know how you get this "marker" idea. But, low variability idea seems ok. You should still discard using phylogeny as it's not used in the study. I'm confused because later, you seem to be using the correct notion of marker.
QUOTE(fcharton @ Oct 23 2006, 03:34 PM) [snapback]4856813[/snapback]
The only aspect which is more difficult is to be able to date these mutations, as it implies the estimation of a very low probability, and slight changes in the estimate can produce big changes in the derived chronology.
Not following you. What estimate are you talking about? Again, you are going even farther to say that mere assumptions must be an integral part of phylogeny. But we already ruled out the possibility of using phylogeny, didn't we?
QUOTE(fcharton @ Oct 23 2006, 03:34 PM) [snapback]4856813[/snapback]
A short observation is passing, the results you quote here correspond to a total sample of 383 persons… What happened to the 458 others? (more than half of the sample)
Now, the first thing I’d like to observe is that if the populations were as homogeneous as you seem to say, then the marker would either be present or absent in all a population (except probably in the “original source”) the fact that you can measure something like 4 out of 13 on the Japanese, or 3 out of 68 for Europeans, shows that inside each of these populations, there is some diversity, ie people with and people without the marker.
A seemingly correct observation of facts. But if you are interested in diversity research, this should not be a study you focus on. Take korean Y study I posted, if you like to discuss farther.
QUOTE(fcharton @ Oct 23 2006, 03:34 PM) [snapback]4856813[/snapback]
This is where the law of large numbers sets in, it gives probabilities that this is likely or unlikely to happen, but it needs larger samples.
Just as an example, if I aggregate a bit more the information:
Suppose I try to “recut” the sample into Africans, Europeans, Northern Asians and Southern Asians, I get
Africans 37/72
Europeans 3/68
Northern and western Asians (Chinese, Japanese, Tibetans, West Asians) 9/65
South+SouthEast Asians 0/178
Again. you are following the wrong assumption on the study, although the division is probably more appropriate than the original study.
QUOTE(fcharton @ Oct 23 2006, 03:34 PM) [snapback]4856813[/snapback]
I get observations which are slightly less probant. Note though that I didn’t doctor the data, I tried to find groups which are geographically close.
This, in my opinion, is one reason why sampling is important, especially when dealing with relatively rare events (such as the prevalence of this marker), and this is where the law of large number (weak, strong, or uniform) applies.
My second concern is linked to the methodology itself. If I were to take the test, I'd count as French, so far up in my family tree I look, we are all French, and besides, I look very French. The problem is that one of my ancient male ancestors could well not be French, in which case I could have the "wrong" Y marker. But the test would detect this, you might say. Or would it? Suppose only four French were tested, the test might also conclude that this marker is present to some proportion in the French population. My problem is that you cannot use the measured quantity as a way to detect errors in the data. This is strictly equivalent to the outliers one can observe in empirical datasets, which can result from measurement errors, or improbable events. Again, the only solution is to dilute them by increasing sample size.
I can see how you make use of LLN. Interesting as it may be, you made several wrong description. Phenotype (eg, looks) and genotype (e.g., genes) are two different things. In Y-chromosome study, there is only a genotype. But I honestly think that this is a trivial use of LLN, as, in most studies, we do have sufficient number of samples, and idea of outliers sounds rather artificial.
QUOTE(fcharton @ Oct 23 2006, 03:34 PM) [snapback]4856813[/snapback]
Finally, a problem can happen if the original sample is biased (ie if the 13 japanese, or the 23 chinese, had some particular characteristic which made the result wrong, like them being less, or more, related (family wise) than they should in a pure random setting. The problem here is with the constitution of the sample. Ask any pollster about it, he'll probably tell you that achieving purely random samples is a daunting tasks, because biases tend to creep in many unexpected fashions, especially when the sample is small. Again, the only solution to this problem is having larger samples.
Study objective is not to conclude about the absence of YAP+ in chinese, that part of work on individual population is reserved for another research which I cited in the first page of this thread.
In summary, this article is not my liking at all. That's why I cited only in response to herousabi's request. I justified the study's perspective, and general philosophy of the researches, but there seems to be better ways to do it. I pointed out that their methods are sufficient for their study and objective, as you rather carelessly criticizes the study.