Tuesday 19 June 2012

Prosecutor fallacy again in media reporting of David Burgess DNA case

There are numerous reports today of the trial of David Burgess accused of killing Yolande Waddington in the 1960s. Burgess had been ruled out as a suspect at the time of the crime because his blood was found not to match that of blood on a sweater belonging to Yolande. However, new DNA analysis has found that Burgess's DNA profile does match that of blood found on a sack that was at the crime scene.

Following on from previous blog postings it is clear that again reporters are making the prosecutor fallacy even though it appears not to have been made in court (but as I explain below I believe that other errors were made in court). For example, the Sun provides a classic example of the prosecutor fallacy:
Scientists said the chances of the DNA on the sack not belonging to him were less than “one in a billion”. 
However, both the Mail and Guardian report what I assume were the actual words used by the forensic scientist Mr Price in court:
... the probability of obtaining this result if it is due to DNA from an unknown person who is unrelated to David Burgess is smaller than one in a billion, a thousand million.
Ignoring the fact that all kinds of testing/cross contamination errors have not been factored in to the random match probability of one in a billion, then there is nothing wrong with the above statement because if we let:

  • H be the hypothesis "DNA found at scene does not belong to defendant or a relative".
  • E be the evidence "DNA found is a match to defendant".
Then the probability of E given H (which is what is stated in the above quote) is indeed one in a billion.

But what is VERY interesting is that Burgess was ruled out in the original investigation because his blood type did NOT match the sample from the scene. To explain the 'change' we get the following quote in the Guardian article:
"Mr Price said the initial test on the bloodstained sweater may have been flawed and that the difference between Burgess’s blood type and that found on the sweater could be due to a mistake in the process that was known to occur sometimes."
In other words the forensic scientist claims that the lack of a positive blood match first time round is "due to a mistake in the process" but he appears never to consider the possibility of any mistake in the process leading to a positive DNA match. Perhaps conveniently for the CPS it appears the sweater has somehow got 'lost'  (curious how that crucial crime scene item should vanish whereas the sack which was never tested orginally should remain) so there was no attempt to test the DNA of the blood on the sweater.

If the latest ruling from the USA is anything to go by, there is going to be even less less chance of questioning the accuracy of DNA and other types of forensic analysis in future.


  1. in March, a de facto spokesperson for REvil who goes by the pseudonym Unknown claimed they would never voluntarily quit ransomware.

  2. Even if the U.S. was able to successfully either knock REvil offline or convince Putin to crack down on it, other ransomware groups are still active, and not all ransomware hackers are in Russia.

  3. In a call Friday afternoon with reporters, a senior administration official, speaking on the condition of anonymity, said the White House's official position is that tackling the problem of Russia harboring ransomware hackers could take at least six months.

  4. "This is more than just a conversation taking place between the two leaders," the official said. "This is a broad campaign, and it won't have an immediate on-off effect, like a light switch."

  5. The U.S. Federal Aviation Administration (FAA) has warned Elon Musk's space company SpaceX that its environmental review of a new tower at its Boca Chica launch site in Texas is incomplete and the agency could order SpaceX to take down the tower.

  6. An FAA spokesman said on Wednesday that the agency's environmental review underway of SpaceX’s proposed rocket assembly "integration tower" is "underway," and added that "the company is building the tower at its own risk."

  7. A May 6 letter from the FAA to SpaceX seen by Reuters said recent construction activity on one of the two proposed towers "may complicate the ongoing environmental review process for the Starship/Super Heavy Launch Vehicle Program." The FAA letter said the tower could be as high as 480 feet.

  8. Based on the environmental review, the FAA could order SpaceX to take down the tower. "It is possible that changes would have to be made at the launch site, including to the integration towers to mitigate significant impacts," the May 6 letter said, adding the FAA learned of the tower's construction "based on publicly available video footage."

  9. I have read your article; it is very informative and helpful for me. I admire the valuable information you offer in your articles. 토토

  10. These are in fact impressive ideas in on the topic of blogging.
    You have touched some nice things here. 토토

  11. Your website deserves all of the positive feedback it’s been getting. I will be back soon for further quality contents. 온라인카지노

  12. https://gamebegin.xyz You are able to practice by yourself. A pitching machine allows you to set the speed in the soccer ball. By loading a number of baseballs into the machine, you can practice hitting without the need for a pitcher. This electronic equipment is good for these who want to process baseball on your own. Pitching equipment may be acquired at the neighborhood sporting products retail store.

  13. https://gameeffect.xyz Many individuals have loved the overall game of baseball for a long time. You will find fans around the globe, from dedicated small-leaguers to perish-hard spectators. This article has ideas to demonstrate how satisfying baseball happens to be.

  14. オンライン カジノ ビットコイン The thing is them on magazines and on Television set, women and men who look like their forearms and thighs will explode since their muscle tissues are extremely big! There is absolutely no will need that you can consider your body for that level when you don't prefer to, since the simple techniques in the following paragraphs will assist you to construct muscle mass within a wholesome method.

  15. https://gamezoom.xyz Finding a workout companion can considerably boost your muscle mass-creating final results. Your companion could be a useful method to obtain determination for adhering to your workout treatment, and pressing you to improve your endeavours while you figure out. Developing a reputable partner to sort out with can also help help keep you harmless simply because you will invariably possess a spotter.