FDC Statistical Analysis & Population Genetics 3

Question 1

Which statistical concept describes the probability that stochastic effects (e.g., allele dropout) could cause a heterozygous contributor to appear homozygous in low-template DNA analysis?

Accepted Answer

Allele dropout probability

Answer

Allele dropout probability quantifies the likelihood that one allele of a heterozygous contributor fails to amplify above the detection threshold, a critical consideration when interpreting low-template or degraded DNA profiles.

Question 2

When reporting forensic DNA statistics as a verbal equivalent, which body's guidance recommends terms such as 'extremely strong support' or 'very strong support' to accompany likelihood ratio values?

Accepted Answer

The European Network of Forensic Science Institutes (ENFSI)

Answer

ENFSI has published guidelines recommending a verbal equivalence scale for LR values that allows analysts to communicate the strength of statistical evidence in plain language alongside numerical results.

Question 3

The 'prosecutor's fallacy' in DNA statistics refers to incorrectly interpreting the RMP as:

Accepted Answer

The probability that the defendant is innocent, when it actually represents the frequency of the profile in the population

Answer

The prosecutor's fallacy transposes the conditional probabilities, equating P(profile | innocence) with P(innocence | profile), which is an incorrect logical leap that dramatically overstates the evidential weight of a DNA match.

Question 4

Which of the following correctly describes the relationship between Fst and within-population allele frequency variance in a structured population?

Accepted Answer

Higher Fst indicates greater allele frequency differentiation between subpopulations, requiring larger theta corrections

Answer

Fst measures the proportion of total genetic variation attributable to differences between subpopulations; higher Fst indicates greater substructure, which justifies using a larger theta correction to avoid underestimating profile frequencies.

Question 5

In probabilistic genotyping of mixtures, a deduced genotype likelihood ratio (DGLR) is preferred over the combined probability of inclusion (CPI) primarily because:

Accepted Answer

DGLR evaluates the evidence for a specific individual's genotype rather than assuming all consistent genotypes are equally likely

Answer

DGLR (or LR from probabilistic genotyping) assigns weight to specific genotype combinations based on the observed peak height data and models, making it more discriminating than CPI, which treats all consistent genotypes as equally probable.

(FDC) Forensic DNA Certification Practice Test

(FDC) Forensic DNA Certification Practice Test

FDC Statistical Analysis & Population Genetics 3