Monday, June 21, 2010

How Lawyers Lie With Statistics

Vision Forum willfully distorted statistics related to the true morbidity and mortality associated with ectopic pregnancy.  Ectopic pregnancy still remains the leading cause of death of all pregnant women in the first trimester of pregnancy.  It accounts for 9% of all maternal deaths in all pregnancy-related deaths.  In the case of death of pregnant women which includes non-pregnancy related death (unrelated heart disease or car accidents, for example), ectopic pregnancy still accounts for 6% of deaths of pregnant women.  

Despite these statistics, Vision Forum and Samaritan Ministries insist that ectopic pregnancy does not pose a significant health risk to women.  They have offered that 60-100 cases of live births resulting from ectopic pregnancies have been documented, but I can find no such reference to this rate of frequency.  One rate of frequency of "one in 60 million" has been offered to describe the rate of such births, and many falsely understand this as a probability statement when the probability for such births is actually ZERO.  I believe that the publications produced on this topic also capitalize on frequencies, using them as probability statements.  In the absence of well-rounded data presenting all the statistics, both Vision Forum and Samaritan Ministries manipulate trusting readers to accept a dangerous view of a very serious medical problem experienced by women of childbearing age.  Ectopic pregnancy, a deadly threat to women, should not be viewed as a game of chance.

Note how attorneys alter the way they present information to juries in order to make statistics seem either more or less impressive.  It is my hope that the reader will come away with a greater appreciation for the language of medical statistics and how numbers can be used to deceive the unsuspecting.

Excerpts from

South California Law Review, Vol. 74, p. 1275, 2001
(emphasis mine!)

Consider the following four formulations of a one in one thousand DNA match statistic that might appear in a criminal case:

1. The probability that the suspect would match the blood specimen if he were not the source is 0.1%.

2. The frequency with which the suspect would match the blood specimen if he were not the source is one in one thousand.

3. One tenth of one percent of the people in Houston who are not the source would also match the blood specimen.

4. One in one thousand people in Houston who are not the source would also match the blood specimen.

These four formulations are legitimate, mathematically comparable ways to describe a one in one thousand DNA match statistic. However, they are psychologically different and their effect on jurors varies significantly. . .

The bottom line appears to be this: When the statistic is framed in the language of probability (e.g., 0.1%) in a way that highlights a particular suspect’s chance of matching by coincidence, it tends to be persuasive. . . . In short, DNA match statistics that seem impressive when presented one way seem insufficient when presented another way. . . 

The results dramatically illustrate that the persuasive power of DNA evidence may depend, in part, on how the match statistics are presented and framed. . .

Although the different ways of presenting the DNA match statistic offered here are legitimate, they may not be equally likely to produce a proper weighting of the DNA evidence. As noted earlier, previous research suggests that jurors underweight statistical evidence, including DNA evidence. This would seem to bolster the argument that evidence should be presented in s/p rather than m/f form because the former is associated with greater perceived weight for the DNA evidence.

On the other hand, studies also show that people reason better with statistical data that are presented as frequencies rather than as probabilities. People are not only more likely to reason in accordance with the logic of probability theory with frequencies than with probabilities, but a frequency presentation decreases the risk that people will subscribe to various statistical fallacies. . .

One reasonable solution is to employ frequency presentations in which efforts are made to discourage people from devaluing the DNA evidence on grounds of nonuniqueness. Alternatively, decisionmakers could be informed that there are different ways of presenting the same statistical information. . . 

This paper began with the assertion about the well-known power of DNA analysis in the courtroom. I caution that this power is a theoretical one. In practice, DNA analyses produce statistics that may or may not persuade jurors about whether a particular person is the source of a particular sample. 

The studies offered here suggest that the persuasive value of DNA evidence may depend as much on an understanding of the psychology of numbers as it does on the underlying science and the statistical expression of that science. 

~~~End of cited work~~~

Cindy suggests:
(That's why you should stick to obtaining medical advice from physician and nurses, making decisions about your health with your own physician.  It is best not to seek such information from an attorney with an agenda.)