Statistics

Statistics and statistical concepts frequently appear in court-usually introduced by expert witnesses. Absent a basic understanding of the language of statistics, attorneys and judges may allow invalid and unreliable opinions and conclusions into legal proceedings–with egregious consequences.

Chapter 4 of The Litigator’s Handbook of Forensic Medicine, Psychiatry, and Psychology is designed to arm jurists and lawyers with the foundation necessary to identify proper (and improper) statistical methods and their application to ensure that only reliable and valid statistical evidence is presented to the finder of fact. Written by two forensic neuropsychologists (one of whom is also an attorney in the USA), this chapter aims to be as far from dry and sleepy as possible, with whimsical real-world vignettes to help illustrate statistical concepts. Particular topics include: 

•  Primers on the most common statistical concepts, covering everything from variables, populations, samples and causation & correlation to statistical significance, effect size and the varieties of bias.

•  Thorough discussion of validity, including face, content, construct, internal, external, statistical conclusion and criterion-related 

•  Thorough discussion of reliability, including test-retest, interrater and internal consistency 

•  Particular discussion of the unique language of statistics in psychological assessment, including norms, normal and non-normal distribution, standard deviation, percentiles, t-scores, z-scores, standard error, confidence level, confidence interval, differential diagnosis, chi square, ANOVA and regression 

•  Primer on probability, including Bayes’ Theorem, error rates, base rates, sensitivity, specificity, likelihood ratio, predictive values, relative risks and odds ratio 

As an aid to better understanding these statistical concepts, the chapter also includes illustrative case digests from numerous jurisdictions that demonstrate: (1) properly performed and introduced statistical concepts; (2) faulty statistical “junk science” that was allowed into proceedings; and (3) examples of seriously faulty statistical evidence that was foisted upon decision-makers and fact finders.

By providing attorneys and judges with a firm footing in the full range of statistical concepts relied on by medical, psychiatric and psychological professionals, this Uses (and Misuses) of Statistics in Courts of Law chapter is an invaluable guide for navigating the perplexities of this type of evidence.