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General => The Common Room => Topic started by: melba_schmelba on Thursday 21 April 22 19:52 BST (UK)
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If the supposed average rate of illegitimacy is 5% - does that mean, in 10 generations i.e. on average, about 300 years, the likelihood of your ancestor in the male line being someone of a different surname is 50%? And in 600 years, it is almost certain that one of your male ancestors would have had a father who was not who he was meant to be (or they inherited their mother's surname) :o?
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If the supposed average rate of illegitimacy is 5% - does that mean, in 10 generations i.e. on average, about 300 years, the likelihood of your ancestor in the male line being someone of a different surname is 50%? And in 600 years, it is almost certain that one of your male ancestors would have had a father who was not who he was meant to be (or they inherited their mother's surname) :o ?
I don't think so. Surely "average rate" implies across the generations. Regardless of the number of generations, the percentage remains the same.
Regards
Chas
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This post is so interesting, I am clueless with the most basic things but I never contemplated the rates of illegitimacy or anything else to do with the subject. My maternal grandmother was as far as I know born as an illegitimate child and trying to find out who her mother and father were but struggling. I hope you can find out what you desire
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If the supposed average rate of illegitimacy is 5% - does that mean, in 10 generations i.e. on average, about 300 years, the likelihood of your ancestor in the male line being someone of a different surname is 50%? And in 600 years, it is almost certain that one of your male ancestors would have had a father who was not who he was meant to be (or they inherited their mother's surname) :o ?
I don't think so. Surely "average rate" implies across the generations. Regardless of the number of generations, the percentage remains the same.
Regards
Chas
Ah, but I am not talking about the probability of each event individually, I am talking about the accumulated probability over many generations that at least one ancestor in the male line will have been illegitimate :).
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I'm no expert so don't quote me but I get the impression that the likelihood of ancestors having different surnames over the periods of time you gave as an example or over any time would be expected and I would think that illegitimacy doesn't really come into it in the respect of the illegitimacy rate and different surnames.
I may be wrong as I say but my maternal grandmother was born illegitimate and the amount of different surnames that have cropped up over a 300 year period are vast lol I think that possibly the illegitimacy rates have changed over the years for many reasons
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This post is so interesting, I am clueless with the most basic things but I never contemplated the rates of illegitimacy or anything else to do with the subject. My maternal grandmother was as far as I know born as an illegitimate child and trying to find out who her mother and father were but struggling. I hope you can find out what you desire
Well, I wasn't really talking about a specific event of illegitimacy Joby (although I do have several instances in my tree) :), I was just speculating really, considering we can now get Y-DNA tests (but also a basic Y-DNA result from 23andme or LivingDNA) and we can find out if we match other people of our surname, or might get a surprise and find we don't match people of our surname but lots of people of another (talking specifically of a FTDNA Y-DNA test that would give that ability). I know for example someone doing a surname study and has noticed that several branches have the same Y-DNA but some do not (but have no knowledge of any illegitimacy in their ancestry).
I may be wrong as I say but my maternal grandmother was born illegitimate and the amount of different surnames that have cropped up over a 300 year period are vast lol I think that possibly the illegitimacy rates have changed over the years for many reasons
I was meaning in the male line specifically :), in DNA terms that is only something men can test for (a woman could get her brother/father/uncle to test to find out a Y-haplogroup associated with their father's male line). I am sure illegitimacy rates have varied, especially when lots of men died, i.e. in the World Wars, or if you had female ancestors who lived in a war zone - Genghis Khan and his soldiers left a traceable genetic imprint all the way to Eastern Europe I believe.
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If you don't mind me asking and it is purely out of genuine interest,... What exactly is it that you want to find out using the illegitimacy rate over a certain period to understand if the family surnames would differ? I just can't see how they can both be an avenue to go down or a method that may take you off track so to speak. Please don't think I am questioning you or anything impolite, I really am interested in this post as I love these kind of things
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If you don't mind me asking and it is purely out of genuine interest,... What exactly is it that you want to find out using the illegitimacy rate over a certain period to understand if the family surnames would differ? I just can't see how they can both be an avenue to go down or a method that may take you off track so to speak. Please don't think I am questioning you or anything impolite, I really am interested in this post as I love these kind of things
Just curiosity Joby, not trying to trace anything specifically :). Many people are quite attached to their surnames, but the truth may be that, after a certain amount of time, your ancestor in the male line being someone of a different surname will be quite likely. If you had a known illegitimacy in your recent male line, or you were a man who was adopted for example, in that case you might be particularly interested in getting a Y-DNA test, but the in depth tests can be expensive, i.e. FTDNA's most expensive test the Big Y-700 FTDNA is currently on sale at £290
https://www.familytreedna.com/products/y-dna
It would allow you to have in depth matching to others in the FTDNA database and you might be lucky to have an exact match, but often people don't. But there would be other things you could do, i.e. look at your 23andme matches to see if you could see a pattern in close matches in their Y-DNA.
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I feel I should confess that I have no idea whatsoever what you are on about reading the varying DNA tests you mentioned lol I have been trying to find out information about the birth mother of my maternal grandmother who was illegitimate and adopted aged two
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I feel I should confess that I have no idea whatsoever what you are on about reading the varying DNA tests you mentioned lol I have been trying to find out information about the birth mother of my maternal grandmother who was illegitimate and adopted aged two
In your case a standard (autosomal) test as Ancestry or 23andme offer would be your best bet for that Joby :), then upload the tests to MyHeritage, FTDNA and GEDMATCH, and on GEDMATCH you could combine the two kits for better accuracy.
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You sound amazingly intelligent and I love the idea that I am of a decent standard of intelligence but times like these are quite sobering lol is your knowledge based on self teaching or are you as I expect some form of scientist?
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Ah, but I am not talking about the probability of each event individually, I am talking about the accumulated probability over many generations that at least one ancestor in the male line will have been illegitimate :).
As well as the illegitimate ones - born of an unmarried mother - don't forget the others born of a married mother but an unrelated father ;) So after 10 generations I guess a genuine family line as documented may be pretty rare ....
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You sound amazingly intelligent and I love the idea that I am of a decent standard of intelligence but times like these are quite sobering lol is your knowledge based on self teaching or are you as I expect some form of scientist?
LOL no Joby, just a genealogy geek :) who has learnt from forums like this, blogs, vlogs, Rootstech, and yes, even books ;D. I am sure some on here are far more qualified as far as mathematics are concerned.
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Ah, but I am not talking about the probability of each event individually, I am talking about the accumulated probability over many generations that at least one ancestor in the male line will have been illegitimate :).
As well as the illegitimate ones - born of an unmarried mother - don't forget the others born of a married mother but an unrelated father ;) So after 10 generations I guess a genuine family line as documented may be pretty rare ....
Well yes exactly :o. So even after 150 years, there is probably a 25% chance that your male line originated in someone with a different surname, so it really is going to be something quite common for a lot of the population to potentially find out when doing DNA testing and genealogy and comparing your DNA test to someone of the same surname, someone you suppose to be a 3rd cousin but DNA suggests are not.
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I can't help thinking that the maths is adding to confusion but I have that thought possibly because I may misunderstand the point of the illegitimacy rate compared to surnames which is of course down to moi! Lol
I am very new to all this stuff but with politeness, charm and whatever else I can conjure up.... I hope people will take pity and help me lol
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If the supposed average rate of illegitimacy is 5% - does that mean, in 10 generations i.e. on average, about 300 years, the likelihood of your ancestor in the male line being someone of a different surname is 50%? And in 600 years, it is almost certain that one of your male ancestors would have had a father who was not who he was meant to be (or they inherited their mother's surname) :o?
An average of 5% remains as 5% irrespective of the number involved.
The base number might change but an Average percentile remains static
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I can't help thinking that the maths is adding to confusion but I have that thought possibly because I may misunderstand the point of the illegitimacy rate compared to surnames which is of course down to moi!
The illegitimacy rate should indicate 'births out of wedlock', or Base-born as cantankerous clerics used to write. Some of those (quite a few today) may have the true biological father, the parents having regularised the situation later. There is one on my wife's tree, who was subject to a bastardy order, but the father came round and made an honest woman of the mother.
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If the supposed average rate of illegitimacy is 5% - does that mean, in 10 generations i.e. on average, about 300 years, the likelihood of your ancestor in the male line being someone of a different surname is 50%? And in 600 years, it is almost certain that one of your male ancestors would have had a father who was not who he was meant to be (or they inherited their mother's surname) :o?
An average of 5% remains as 5% irrespective of the number involved.
The base number might change but an Average percentile remains static
I don't think this is correct. Think of it this way......
there is a game in which you have a 5% chance of winning - if you play once, you have a 5% chance to win, but if you are allowed to pay twice, you have a 10% chance you will eventually win, play four times, a 20% chance etc.
Similarly if you are baby that is born, there is 5% chance your father will not the person whose surname you bear. If you think of each birth as a separate but linked event, the chance increases the number of 'tries' at this game that occur.....
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I don't think this is correct. Think of it this way......
there is a game in which you have a 5% chance of winning - if you play once, you have a 5% chance to win, but if you are allowed to pay twice, you have a 10% chance you will eventually win, play four times, a 20% chance etc.
No, in the example you give the probabilities of winning each game remain at 5% regardless of how many times you play - the percentages aren't stacked up in that manner.
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I don't think this is correct. Think of it this way...... there is a game in which you have a 5% chance of winning - if you play once, you have a 5% chance to win, but if you are allowed to pay twice, you have a 10% chance you will eventually win, play four times, a 20% chance etc.
You'll have to modify your maths a bit, as if you play your game 20 times you are certain to win ;D Overall probabilities are usually rather less simple than you think ;)
Family history records are always beset by the snag that informants often gave the info that the recorder wanted to hear, and there was usually no way to verify anything, even if needed.
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I don't think this is correct. Think of it this way......
there is a game in which you have a 5% chance of winning - if you play once, you have a 5% chance to win, but if you are allowed to pay twice, you have a 10% chance you will eventually win, play four times, a 20% chance etc.
No, in the example you give the probabilities of winning each game remain at 5% regardless of how many times you play - the percentages aren't stacked up in that manner.
I am not talking about winning each game ;D, I am talking about eventually winning. And surely the more times you play a game, the more times you throw a dice, the more likely it becomes the more times you do it, that you will eventually win or get the right number :).
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Well, I think I have possibility found the correct equation
https://math.stackexchange.com/questions/1894684/what-is-the-chance-of-rolling-a-specific-number-after-a-certain-amount-of-rolls
1−(1−1/x)y
this referring to the probability of getting a 6 on a six sided dice after six rolls
So (I think) using the same logic, thinking of ten generations where there is a probability of 5% that the child will have a father of a different surname
1 - (1-(5/100))10 = 0.40
i.e. I think the chance in 10 generations that you will have an ancestor in the male line of someone who was born to someone of a different surname is 40%??
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Some more probabilities using the same equation..of an ancestor in the male line having a surname different to their biological father
in 20 generations i.e. approx 600 years = 64%
in 5 generations i.e. approx 150 years = 23%
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If the supposed average rate of illegitimacy is 5% - does that mean, in 10 generations i.e. on average, about 300 years, the likelihood of your ancestor in the male line being someone of a different surname is 50%? And in 600 years, it is almost certain that one of your male ancestors would have had a father who was not who he was meant to be (or they inherited their mother's surname) :o?
No, because the statistics do not show that they" show-" Illegitimate births accounted for 4–6 per cent of recorded births between 1860 and 1930 (40,000–65,000 a year).
So for the sake of simplicity round the percentage to 5%.
That is still not an average percentage of births by the married population as it includes many births by single women, in addition it does not take into account how many women have more than one illegitimate child, some have 5 or 6.
In a similar way some married women have one child by a father who is not their husband, some have more than one child by the same man who is not their husband and others have multiple children by multiple men who are not their husband.
Some have one, then marry the father which these days legitimises the birth.
To even try to compute the chance that a child was not the child of the husband the figures would have to be far more detailed.
Cheers
Guy
PS This is not the same calculation for a dice as the dice having 6 sides has a limited number of possiblilities.
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I think my family buck the trend?!
My paternal line has had just the 1 surname (and 1 spelling) from the mid-1500's.
Likewise, my maternal line (as far as my mother) have had the 1 surname, also since the mid-1500's.
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If the supposed average rate of illegitimacy is 5% - does that mean, in 10 generations i.e. on average, about 300 years, the likelihood of your ancestor in the male line being someone of a different surname is 50%? And in 600 years, it is almost certain that one of your male ancestors would have had a father who was not who he was meant to be (or they inherited their mother's surname) :o?
No, because the statistics do not show that they" show-" Illegitimate births accounted for 4–6 per cent of recorded births between 1860 and 1930 (40,000–65,000 a year).
So for the sake of simplicity round the percentage to 5%.
That is still not an average percentage of births by the married population as it includes many births by single women, in addition it does not take into account how many women have more than one illegitimate child, some have 5 or 6.
In a similar way some married women have one child by a father who is not their husband, some have more than one child by the same man who is not their husband and others have multiple children by multiple men who are not their husband.
Some have one, then marry the father which these days legitimises the birth.
To even try to compute the chance that a child was not the child of the husband the figures would have to be far more detailed.
Cheers
Guy
PS This is not the same calculation for a dice as the dice having 6 sides has a limited number of possiblilities.
Hi Guy, the 5% figure came from an estimation that is often quoted, although someone recently suggested 10% (can't remember who) and most people thought that figure was very much over the top. I would be including births by single women, in what I said, as the surname they would pass on to their son would usually not be that of the biological father, unless they later married or had the illegitimate birth accepted by the biological father, which was likely unusual. What I haven't included is adopted people, who often if not usually bear a surname that was not that of their biological father. But I think that would be a figure quite smaller than the illegitimacy rate, I think I found a 67 in 10000 figure earlier which is 0.67%, so it wouldn't affect my calculations too much.
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I think my family buck the trend?!
My paternal line has had just the 1 surname (and 1 spelling) from the mid-1500's.
Likewise, my maternal line (as far as my mother) have had the 1 surname, also since the mid-1500's.
Ah but the point is you can't be sure that the biological father was a person of that surname in every birth of every ancestor on that male line :). Well unless you are part of an in depth surname study, and you have verified that a very very distant cousin who shares the same surname and origins has the same Y-DNA profile.
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If the supposed average rate of illegitimacy is 5% - does that mean, in 10 generations i.e. on average, about 300 years, the likelihood of your ancestor in the male line being someone of a different surname is 50%? And in 600 years, it is almost certain that one of your male ancestors would have had a father who was not who he was meant to be (or they inherited their mother's surname) :o?
No, because the statistics do not show that they" show-" Illegitimate births accounted for 4–6 per cent of recorded births between 1860 and 1930 (40,000–65,000 a year).
So for the sake of simplicity round the percentage to 5%.
That is still not an average percentage of births by the married population as it includes many births by single women, in addition it does not take into account how many women have more than one illegitimate child, some have 5 or 6.
In a similar way some married women have one child by a father who is not their husband, some have more than one child by the same man who is not their husband and others have multiple children by multiple men who are not their husband.
Some have one, then marry the father which these days legitimises the birth.
To even try to compute the chance that a child was not the child of the husband the figures would have to be far more detailed.
Cheers
Guy
PS This is not the same calculation for a dice as the dice having 6 sides has a limited number of possiblilities.
Hi Guy, the 5% figure came from an estimation that is often quoted, although someone recently suggested 10% (can't remember who) and most people thought that figure was very much over the top.
As a note I got the figures from "Illegitimacy in English law and society, 1860–1930" by Ginger Frost published in 2016 by Manchester University Press, ISBN 9781784997441 in case anyone wants to read the very interesting book.
Cheers
Guy
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If the supposed average rate of illegitimacy is 5% - does that mean, in 10 generations i.e. on average, about 300 years, the likelihood of your ancestor in the male line being someone of a different surname is 50%? And in 600 years, it is almost certain that one of your male ancestors would have had a father who was not who he was meant to be (or they inherited their mother's surname) :o?
No, because the statistics do not show that they" show-" Illegitimate births accounted for 4–6 per cent of recorded births between 1860 and 1930 (40,000–65,000 a year).
So for the sake of simplicity round the percentage to 5%.
That is still not an average percentage of births by the married population as it includes many births by single women, in addition it does not take into account how many women have more than one illegitimate child, some have 5 or 6.
In a similar way some married women have one child by a father who is not their husband, some have more than one child by the same man who is not their husband and others have multiple children by multiple men who are not their husband.
Some have one, then marry the father which these days legitimises the birth.
To even try to compute the chance that a child was not the child of the husband the figures would have to be far more detailed.
Cheers
Guy
PS This is not the same calculation for a dice as the dice having 6 sides has a limited number of possiblilities.
Hi Guy, the 5% figure came from an estimation that is often quoted, although someone recently suggested 10% (can't remember who) and most people thought that figure was very much over the top.
As a note I got the figures from "Illegitimacy in English law and society, 1860–1930" by Ginger Frost published in 2016 by Manchester University Press, ISBN 9781784997441 in case anyone wants to read the very interesting book.
Cheers
Guy
Thanks Guy, I understand what you were saying now, thanks for the book recommendation. So if the 5% figure referred to supposed 'bastards' as the authorities deemed them, then perhaps the real figure of NPEs was somewhat higher (i.e. births to already married mothers), and short of doing, or collating the results of already made surname Y-DNA studies I am not sure how we could get close to an accurate figure on that. But whatever the figure is, it does seem that the likelihood within the fairly recent past, of your male line ancestor actually descending from someone not of that surname is higher than many people might expect.
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Thank you to all who posted on this topic, I really am finding the information and explanation's incredibly interesting. You're a clever bunch it must be said! :)
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"does that mean, in 10 generations i.e. on average, about 300 years, the likelihood of your ancestor in the male line being someone of a different surname is 50%?"
No, it doesn't.
For the purposes of argument, let's assume that 5% is an accurate estimate of the illegitimacy rate and that that rate has not changed over time. If you look at ten generations of direct ancestors in the male line, you have a sample size of ten paternity events of which 5% [on average] are likely to be illegitimate. In other words, in that specific line - the one bearing the surname - the likelihood of an illegitimate birth is low, less than one out of the ten.
Obviously, if you consider all of your direct ancestors over ten generations [not just the male line], the chances of an illegitimate birth are much higher. About 50 illegitimacies could be expected [0.05 x 1024 = 51.2].
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"does that mean, in 10 generations i.e. on average, about 300 years, the likelihood of your ancestor in the male line being someone of a different surname is 50%?"
No, it doesn't.
For the purposes of argument, let's assume that 5% is an accurate estimate of the illegitimacy rate and that that rate has not changed over time. If you look at ten generations of direct ancestors in the male line, you have a sample size of ten paternity events of which 5% [on average] are likely to be illegitimate. In other words, in that specific line - the one bearing the surname - the likelihood of an illegitimate birth is low, less than one out of the ten.
Obviously, if you consider all of your direct ancestors over ten generations [not just the male line], the chances of an illegitimate birth are much higher. About 50 illegitimacies could be expected [0.05 x 1024 = 51.2].
Can you explain what exact formula you are using Erato? This formula of getting a six at least once with a six sided dice over six rolls, seemed to be a fit for the scenario, but in this case the probability is 5/100 not 1/6 each time
https://math.stackexchange.com/questions/1894684/what-is-the-chance-of-rolling-a-specific-number-after-a-certain-amount-of-rolls
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0.05 x 10 = 0.5.
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0.05 x 10 = 0.5.
Well isn't 0.5 = 50/100 i.e. 50%, that is the logic used on the above link ;D
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I think my family buck the trend?!
My paternal line has had just the 1 surname (and 1 spelling) from the mid-1500's.
Likewise, my maternal line (as far as my mother) have had the 1 surname, also since the mid-1500's.
Ah but the point is you can't be sure that the biological father was a person of that surname in every birth of every ancestor on that male line :). Well unless you are part of an in depth surname study, and you have verified that a very very distant cousin who shares the same surname and origins has the same Y-DNA profile.
Don't touch DNA!
Had I known this was a DNA thread, I would have ignored it.
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No. It's the estimated number of illegitimate births in the sample. Your sample is ten births. Five per cent of them are likely to be illegitimate. Five per cent of ten is 0.5. Since we can't split people in half, we can just say that the number of illegitimate births is probably less than one.
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There are 2 things getting conflated here, and they really should be separated.
1 - There is the 5%. Out of 100 ancestors, 5 will be illegitimate. I do not know where this percentage came from, but it seems to be accepted as true.
2 - The chances of illegitimacy occurring. Has nothing at all to do with the 5% rate. Believing that it does is how the casinos make their profit. When dealing with chance, particularly human events, the variables are infinite. I believe that the closest we could come to a percentage is 50%. That is to say that the chances are 50/50 in every relationship that illegitimacy will occur.
Regards
Chas
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That is what I couldn't understand regarding the illegitimacy rate being a factor when it comes to surnames over generations, I think it would only complicate the thought process lol
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2 - The chances of illegitimacy occurring. Has nothing at all to do with the 5% rate. Believing that it does is how the casinos make their profit. When dealing with chance, particularly human events, the variables are infinite. I believe that the closest we could come to a percentage is 50%. That is to say that the chances are 50/50 in every relationship that illegitimacy will occur.
Regards Chas[/quote]
Let's call a pregnancy resulting from interaction of the woman with ONLY her partner "Faithful".
Similarly, a pregnancy resulting from interaction of the woman with an extra man is "Unfaithful".
For any ONE pregnancy, THEORETICALLY it is either Faithful or Unfaithful, so there are only two possible states, and one of them is Unfaithful; so the probability of the Unfaithful pregnancy is,
1/2 x 100 = 50%, as you say above.
However, the probability that one-half of all women (total number = N) that give birth as "Unfaithful" is NOT 50/50.
It is (1/2) to the (N/2)th power, i.e., for N = 10 women it is 1 in 64, i.e. 1.56%.
Regards,
JMB
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"For any ONE pregnancy, THEORETICALLY it is either Faithful or Unfaithful, so there are only two possible states, and one of them is Unfaithful; so the probability of the Unfaithful pregnancy is,
1/2 x 100 = 50%, as you say above."
Hogwash. Just because there are only two possible outcomes [faithful or unfaithful] doesn't mean that they are both equally likely. When you buy a lottery ticket, there are only two possibilities - it's a winner or it isn't. That doesn't mean you have a 50% of winning, though.
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"For any ONE pregnancy, THEORETICALLY it is either Faithful or Unfaithful, so there are only two possible states, and one of them is Unfaithful; so the probability of the Unfaithful pregnancy is,
1/2 x 100 = 50%, as you say above."
Hogwash. Just because there are only two possible outcomes [faithful or unfaithful] doesn't mean that they are both equally likely. When you buy a lottery ticket, there are only two possibilities - it's a winner or it isn't. That doesn't mean you have a 50% of winning, though.
Sounds as if someone is comparing this with the spin on an electron (50:50), an entirely different situation :P
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Just looking at the maths:
Assuming that the rate of illegitimate births is 5% among both married and unmarried women, and has stayed constant over the period. This is the only statistic we are given.
That means the probability of any individual being legitimate is 0.95.
Over 10 generations, the chances of ALL of the line being legitimate would be 0.9510, or 0.5987 - call it 60%.
Of course, the illegitimacy rate for births to unmarried women is 100%, which spoils things quite a bit. Traditional written records will usually make these events obvious, while we are still clueless about the proportion of NPEs!
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The amount of secretly illegitimate children, born to a man who was not the mother's husband is about 1 to 2%. So one out of 50 ancestors is probably not a blood ancestor, someone else was. But the openly illegitimate percentage is about 5%. So I say about 6 to 7% of all births were illegitimate, including the open NPE's and the secret NPE's.
One of my 4xgreat grandfathers was illegitimate, and one of my 5xgreat grandmothers was illegitimate, no father listed on baptisms.
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Three of my great great grandmothers were illegitimate - no father named on birth or baptism. That's 18.75%.
However one had her father named on her marriage. The father had left the area soon after the birth if not before, and luckily had an unusual name so I was able to trace him.
Another was from a village where everyone seems to be related to everyone else, so DNA is very unlikely to narrow down a suspect.
The numbers of Bastardy Bonds in the archives hints at a higher illegitimacy rate in the late 18th and early 19th centuries. It was such a common thing that the courts had preprinted forms, with a variant of the form for those cases where the putative father did not show up in court. Some fathers did of course go on to marry the mothers, possibly because it was the cheaper option!
My own paternal line is "officially" documented, mostly in church records, all the way back to my 6xg gf in 1715 - "Abrahamus illegitim filius Patientis Halsted & Abrahami Kersaw amborum Waterside". Patience then went on to marry a different chap called Abraham.