[Extra love]

The question is "A couple has for children, all sons. Does this mean that there is a better chance of a daughter on a fifth pregnancy? Explain your answer."

please help me!

[Yggdrasil]

If you flip a coin four times and it lands on heads all four times, does that mean you have a greater than 50% chance of getting tails on the fifth flip?  In statistical terms, are coin flips independent events, or does the outcome of one flip depend on the outcome of previous flips?

[Bronwen Dekker]

There might even be a case for arguing that the couple is MORE likely to produce another son, as the die is clearly loaded. 

(sorry to change from coins to dice... what do you call a coin that is most likely to land in one way...)

I have spent a few minutes trying to do google and PubMed searches to get some sort of insight into why some families have only-male or only-female offspring. It has not proved easy to get useful answers - perhaps these will be a reasonable starting point or perhaps it is just a coin-toss:

http://www.blackwell-synergy.com/doi/abs/10.1111/j.1469-7610.1996.tb01450.x
http://www.biolreprod.org/cgi/content/full/71/4/1063

Any ideas regarding the following related question:

Does anyone know of any research done on families that seem to only produce children of one gender?

Update (12 April 2007)

PubMed searches

'"sex ratio" offspring' gave some interesting (but unrelated) stuff including:
Birth Order, Sibling Sex Ratio, Handedness, and Sexual Orientation of Male and Female Participants in a BBC Internet Research Project.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=17345165&query_hl=9&itool=pubmed_docsum

'" y chromosome" "sex ratio"' yielded, on looking at the 'related articles' for the really old papers, some quite potentially useful information e.g.:
Length of the follicular phase, time of insemination, coital rate and the sex of offspring
http://humrep.oxfordjournals.org/cgi/reprint/12/3/611

[billnotgatez]

If I recollect my probability theory there is a difference between asking
What is the likelihood that you will get a heads after flipping 4 tails?
And
What would be the expected number of heads in flipping the coin 5 times?