A-11. TECHNICAL OVERVIEW OF KINSHIP

A likelihood ratio is calculated to evaluate putative family relationships and develop some degree of certainty for identity. The likelihood ratio is the statistical calculation that results from the comparison of two hypotheses. For this project, we use this calculation to determine whether a person is related or unrelated to a putative family. This calculation determines how many times more likely a person is related based on the given family relationships (using available genetic profiles) than unrelated. The project uses the software program called DNA View to determine kinship.

Non-DNA information is collected during the interviews. The information considered for the statistical calculations may include but is not limited to the following: an estimate of the total population of children that disappeared as a result of the war, the sex of the disappeared person, the age when they disappeared, geographical data, any memories of the event when they were separated from their family (when available), unique physical characteristics, and any supporting documentation including photos.

The first step in the process is that the genetic profiles of the disappeared persons are compared with family reference profiles. Family reference profiles are the genetic profiles of the family members searching for their disappeared relatives and are stored in a separate database from the profiles of the disappeared persons. By comparing the profile of a disappeared person against the family reference profiles, unrelated families can be discarded and “ potential families ” isolated.

The second step in kinship analysis is to determine if a disappeared person can be statistically linked to a putative family through comparison of their genetic profiles and non-DNA information collected during the interview. Once a potential family has been isolated or a family linked by an investigation, individual kinship analysis is conducted to determine if identity to the disappeared person can be confirmed using all available information. For this Project, kinship is accepted when the statistical calculations indicate a “ posterior probability ” or probability of identity of at least 99.9 percent. The “ posterior probability ” or probability of identity is reached using both the statistical likelihood ratio calculation and the non-DNA information that may presumptively associate a disappeared person to a family.

Through years of investigation Pro-Búsqueda determined that approximately 30,000 children had disappeared as a direct result of the wars throughout Central America during the decade of the 1980’ s and years surrounding it. This estimate of the population of disappeared persons is the baseline number used as the non-DNA information accounted for in each statistical calculation. This is referred to as “ prior odds. ” The likelihood ratio is calculated from the DNA information or genetic profiles and the “ prior odds ” calculated from non-DNA information obtained through the interviews conducted by Pro-Búsqueda. Together both calculations are used to determine the “ posterior probability ” or probability of identity for each family relationship evaluated and an identification is made when 99.9 percent is obtained.