When the Sally Clark case was first in the news, I sent the following to Allstat:
I thought members might be interested in some data. In 1996, the most recent
year for which data are available, there were 649,489 live births in E&W.
There were 4,959 deaths in the first year of life, including 394 sudden infant
deaths (SIDS or cot deaths) and 14 homicides. Thus the probability of a cot
death is 1 in 649489/394 = 1,648. If deaths were independent, which they are
not because there are familial risk factors, the risk that a family of two
babies would have two cot deaths would be 1 in 1,648*1,648 = 2,715,904.
Presumably some other adjustment was applied for social factors as the figure
given in the press is said to apply to `well-to-do families'.
The same calculation for homicide gives a risk that that two babies will both
be murdered as one in (649489/14)^2 = 2,152,224,291.
I thought that the figure of 1 in 73000000 was far too small a probability,
whatever it purported to be the probablity of..
Martin
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J. Martin Bland
Prof. of Health Statistics
Dept. of Health Sciences
Seebohm Rowntree Building Area 2
University of York
Heslington
York YO10 5DD
Email: [log in to unmask]
Phone: 01904 321334
Fax: 01904 321382
Web site: http://www-users.york.ac.uk/~mb55/
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