Table of contents

  1. The problem
    1. Role
    2. Scope of the problem
    3. DNA modalities
  2. Simulations
    1. Conclusions


In search of the disappeared children
Asociación Pro-Búsqueda de niñas y niños desaparecidos
Physicians for Human Rights, 1994 press release
Physicians for Human Rights, 1995 press release
Chromosomal Labs, Inc
Forensic mathematics home page
Comments and inquiries are welcome (see home page for email)

Niñas y niños (possible adoptees) interested in finding their biological families –

I suggest you contact Rachel Shigikane, Human Rights Center UC Berkeley, phone 1-510-643-2713. rshig (at sign) berkeley (dot) edu

Reuniting El Salvador families

  1. The problem
  2. From about 1980 to 1992 many small children were taken to orphanages when their when families were disrupted and separated in the civil war (El Salvador human rights practices, 1993). The organization Pro Busqueda (see links) attempts to reunite the children, many of whom were adopted into the United States, with what remains of their biological families. Among the efforts in support of Pro Busqueda is a volunteer DNA identification program led by a group of DNA analysts of the California DOJ, Jan Bashinski DNA laboratory in Richmond, Ca.
    has very generously agreed to perform DNA typing pro bono.

    1. Role
    2. I volunteered to assist, feeling that the problems of matching children with their relatives is very similar to the problem of identifying mass disaster victims. I've participated in or advised many related projects and developed various kinds of software – especially as part of the World Trade Center identification project – which I believe will be helpful with the family associations in El Salvador.

      Update – July 2006 visit to San Salvador

      Four days in San Salvador gave me a chance to meet the dedicated staff of ProBusqueda and to learn a lot more about the history – the nature of the civil war that caused the desaparecidos – the technical and political difficulties and process involved in finding and reuniting children families, and the process of human rights work.

      Our contingent included Physicians for Human Rights, Human Rights Center (UC Berkeley), and DNA folks.

      14,000 missing children?

      Among other things, data given to me extrapolates that the total number of children adopted out of the country in the 80's may be about 14,000.

      These software facilities are

      The main reason for this web page is to present some simulations that we have done.

    3. Scope of the problem – estimates
    4. There are about 500 families with reported missing children, a total of about 700 children. For our present estimates, we simplify that there are merely N=500 children, for now mostly ignoring the extra 200.

      We tentatively assume that three factors will help narrow the search:

      1. sex
      2. approximate year of birth
      3. approximate year of entering the orphanage
      Assuming that both the biological and the adoptive families know those three data, then perhaps that typically reduces the possible (original) identities for a particular adoptee down to 10 choices (factors of 1/2, 1/5, 1/5). Subject to revision, we've made some calculations taking 1/10 as the prior probability.

      We've also decided, as a working criterion, to aim for 99.9% probability for each identification. Since

      Posterior odds = (likelihood ratio)(prior odds),
      99.9% is posterior odds of 1000, and the prior odds are about 1/10 (easier to deal with than 1/9), this means that we need roughly
      likelihood ratio > 10,000.

      The workers in El Salvador are in the process of locating the biological relatives. Sometimes extra relatives are available but hard to get to. We would like to give them guidelines as to what combination of relatives is likely to be adequate.

    5. DNA modalities

  3. Simulations
  4. The simulations are based on Identifiler, and "Hispanic" populations for allele frequency estimates.

    The simulation procedure is to

    The average posterior probability seems like a sensible summary statistic. Usually the simulated likelihood ratios have a very large range, such as from 100 to billions. The worry is how often do the small values occur? If 10% of simulations give a relatively small likelihood ratio, then that represents a 10% chance to be uncertain about the identification. Whether the large values are in the millions or the trillions doesn't much matter. And that is the way the average posterior probability works – it is mostly a measure of the less successful simulations.

    The chart below summarizes the results for the various combinations of relatives that we have considered.
    Family referencesProbability of identity
    (Mean posterior probability at 10% prior)
    one full sibling92.1%
    sibling and aunt94.4%or sibling and uncle
    sibling and two sister aunts97.8% i.e. the aunts or uncles are either both maternal or both paternal
    sibling, aunt, uncle different sides99.8% e.g. maternal aunt, paternal uncle
    sibling and half sibling98%
    sibling and two half siblings99.4% all children share mother; half-siblings share father with one another
    two siblings99.91%
    one parent99.9%ignoring mutation
    sibling and parent99.996%
    father and one half sibling99.95%maternal half-sibling
    father and two half siblings99.996%maternal half-siblings of course
    father and aunt99.993%maternal aunt (else why bother)
    three grandparents96.7%
    four grandparents99.99%surprise – big bonus for all four
    three grandparents and sibling99.994%
    The children were generally at most 12 when taken, so none of them left children of their own in El Salvador that can be considered as references.

    1. Conclusions
    2. We would like to have a very simple set of rules to help the caseworkers decide how many and which relatives they need. Based on the above chart, the rules might look something like –

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