"Feds, Wilson dispute illegal immigrant costs", 15 Sept 1994, SF 
      Examiner, p. A-4.

"Illegal aliens put uneven load on states, study says", 15 Sept 1994, 
      NYT, P. A8.  

"Illegal immigration:  Impact on California", Office of Governor Pete 
      Wilson, press packet, 1994.

"Fiscal impacts of undocumented aliens:  selected estimates for seven 
      states", Urban Institute,  1994.

1.  California initially made the estimate that the annual cost of
hospital emergency care, jails and schools for the undocumented was
around $2.8 billion.  The Urban Institute, however, estimated that
total annual costs were around $1.8 billion (SF Ex, paragraph 5).
After hearing about Urban Institute's report, California released a
new study, with calculations closer to Urban Institute's findings
(NYT, paragraph 7).

2.  The state of California estimates that there are 392,260 illegal
immigrant children being educated in California public schools
(1994-95), whereas Urban Institute believes this figure is at 307,024
(from Table 4.13).  The California figure is found using the Census
Bureau's April 1993 estimate of California's illegal immigrants; this
number is multiplied by the percentage of 5-17 year-old immigrants;
this is then multiplied by the estimated percent attending school.
(from "Methodology for calculating California's costs of educating
illegal immigrants") The Urban Institute uses the same multiplication
process, but it starts out with the estimates from INS 1992 data.
(...)  They also use the Census data to find information on recent
immigrants, and use these as "proxy populations", with the goal of
finding out about the characteristics of the undocumented population.

3.  The two studies get such different numbers because Urban Institute
bases its figures on the INS and California bases its figures from the
Census.  According to UI (pg. 24, 2.3.5), the Census Bureau estimate
is flawed because at the national level, the Special Agricultural
Workers (SAWs) are omitted for the population estimate of legal
residents.  This results in an overstatement of the number of illegal
immigrants in the range of 400,000 to 1,000,000 people.  Because the
INS is focused on immigration issues and the census just tries to
record characteristics for all people in the US, I would tend to think
that the INS puts more care in getting accurate illegal immigration
figures.

4.  These values are slightly different because each agency used a
different school-year for their measurments.  California made
measurments using a projected 1994-95 figure, while Urban Institute
1993-94 figures.  (UI: 1.2.3 and Table 4.13)

(Also, Urban Institute's Table 4.13 shows that UI used a value under 
the heading "State and local per student costs", while California used 
a value under "'Proposition 98' per student costs."  However, in 
California's methodology, they state that they did use the per-pupil 
state and local expenditure level for their estimates, so UI may have 
just incorrectly stated what numbers California used for its 
estimates.)  

5.  Only the SF Examiner gave a description of the reasons for the
different estimates, although it was a brief and incomplete one.  The
article stated "Much of the conflict between California and Washington
revolves around complex data interpretations that defy all but the
most hearty of number crunchers" (paragraph 7, column 2).  The Urban
Institute used Immigration and Naturalization Service estimates for
their analysis, and California officials stated that Urban Institute
researchers did not take into account school debt service and added
payments into the teacher retirement fund.  However, the article does
not state how California calculated its estimates; we only know what
Urban Institute did and why the state of California doubted the
findings.

6.  It is much more difficult to write an article on an economic
analysis because many of these studies are based on forecasting and
estimation.  In surveys, experiments and observational studies,
researchers now what they are looking for and they explain this
explicitly.  As we can see with the immigration articles, there are
many different ways to estimate a value for the cost of a certain
item, such as the education of children.  Thus people who write
newspaper articles on topics such as immigration should try to report
on the concrete evidence in economic studies, but often, this evidence
in uncertain.  It becomes even more difficult when multiple agencies
are working on the same topic.  All the reporter can do is give the
conclusions of each entity, and hope that the entities have collected
data in similar ways.