Understanding Uncertainty - birthdays
http://understandinguncertainty.org/taxonomy/term/315
enDaily Mail gets odds right shock
http://understandinguncertainty.org/node/1253
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p> The Daily Mail and other papers carried the story about <a href="http://www.dailymail.co.uk/news/article-1353586/Mother-Pam-Banell-gives-birth-3-children-date.html" class="external">the Banwell family whose third child shares a birthday, February 5th, with two older siblings</a>, and this time they got the odds right at 133,000 to 1!</p>
<!--break--><p>This example on February 5th was preceded by <a href="http://www.dailymail.co.uk/news/article-1320113/Happy-birthday-Couple-3-children-born-date.html" class="external">the Allali family on October 7th 2010</a>, where the Mail got the odds wrong, and the <a href="http://www.dailymail.co.uk/news/article-518525/Couple-gives-birth-children-day--14-years-apart.html" class="external">MacKriell family on January 29th 2008</a> where they got the odds right - see <a href="/node/891" class="local">our previous blog</a>. As <a href="http://www.badscience.net/2010/02/guns-dont-kill-people-puppies-do/" class="external">Ben Goldacre has discussed</a>, around <a href="http://www.statistics.gov.uk/pdfdir/births1209.pdf" class="external">167,000 third or higher children are born each year</a> in England and Wales - and at least 1 in 135,000 of these should have two older siblings born on the same day (this assumes random birth dates). So we would expect these events to happen with an average gap of less than 12 x 135,000/167,000 = 10 months, or a median of 8 months apart. </p>
<p>I suspect there may have been an unreported case in 2009 - we need some detectives onto this.</p>
</div></div></div><div class="field field-name-taxonomy-vocabulary-2 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Free tags: </div><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/315">birthdays</a></div></div></div><div class="field field-name-taxonomy-vocabulary-7 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Levels: </div><div class="field-items"><div class="field-item even"><a href="/levels/level-1">level 1</a></div></div></div>Sun, 06 Feb 2011 09:49:36 +0000david1253 at http://understandinguncertainty.orghttp://understandinguncertainty.org/node/1253#commentsCoincidence odds are wrong yet again
http://understandinguncertainty.org/node/1240
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>The <a href="http://www.thesun.co.uk/sol/homepage/news/3366983/Third-baby-born-at-exactly-743-for-same-parents.html" class="external"><em>Sun </em>today features a story</a> about a family who have had three children all born at 7.43 (two am and one pm). Heartwarming, but the quoted odds of 300,000,000 to one are sadly wrong.</p>
<!--break--><p>They presumably calculated that there are 60 x 12 = 720 times that could be recorded to the nearest minute (ignoring am or pm). Then they multiplied this up 3 times to get 720 x 720 x 720 = 373,248,000. </p>
<p>But we want the probability of all three being born in the same minute, not of them all being born at 7.43. So the first birth does not contribute to the coincidence - it just sets the 'target' for the other births. So the correct answer is 720 x 720 = 518,400 (even making the probably inappropriate assumption that births are uniformly distributed through the day). And since around 167,000 third children are born in the UK each year, we would expect this event to happen around on average once every three years. So remarkable for the Rigby family, but not that remarkable to hear about. </p>
<p>The <a href="/node/891" class="local">Daily Mail made the same mistake recently</a> with the recurring story of three children being born on the same day. </p>
<p>We've got a lot more on coincidences <a href="/node/62" class="local">here</a>, although it does make us seem a bit miserable, continually puncturing the grand odds being quoted.</p>
<p>(Thanks to Jack Boericke for pointing out this story)</p>
</div></div></div><div class="field field-name-taxonomy-vocabulary-2 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Free tags: </div><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/315">birthdays</a></div></div></div><div class="field field-name-taxonomy-vocabulary-7 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Levels: </div><div class="field-items"><div class="field-item even"><a href="/levels/level-1">level 1</a></div></div></div>Tue, 25 Jan 2011 09:58:03 +0000david1240 at http://understandinguncertainty.orghttp://understandinguncertainty.org/node/1240#commentsStrange how these "1 in 48,000,000" events keep on happening!
http://understandinguncertainty.org/node/891
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>The Daily Mail has a story today about <a href="http://www.dailymail.co.uk/news/article-1320113/Happy-birthday-Couple-3-children-born-date.html">the Allali family whose third child was born on the same date as his two older siblings</a>, claiming that "mathematical experts have revealed that the three siblings have beaten odds of 48 million to one". If these are the real odds, isn't a bit strange how often this story appears in the papers? </p>
<!--break--><p> I am not sure who these mathematical experts are, but their error is pointed out in the comments following the story which correctly assess the odds as 1 in 133,000, assuming every birth day is equally likely. One of the correspondents makes the nice point that around 167,000 'third' children are born each year in this country, and so we would expect to see this story once or twice a year. See <a href="/node/92" class="local">our article on a previous occurrence</a>.</p>
</div></div></div><div class="field field-name-taxonomy-vocabulary-2 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Free tags: </div><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/315">birthdays</a></div></div></div><div class="field field-name-taxonomy-vocabulary-7 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Levels: </div><div class="field-items"><div class="field-item even"><a href="/levels/level-1">level 1</a></div></div></div>Wed, 13 Oct 2010 12:38:18 +0000david891 at http://understandinguncertainty.orghttp://understandinguncertainty.org/node/891#comments