How to Use
the U.S. to Overseas Custom Report 
General Information 
All data
presented in a custom report are statistical estimates,
based on survey responses weighted with data from the
Department of Homeland Security (DHS)
I92/APIS database. The estimates
are subject to a certain amount of error, resulting from the
sampling, data collection, and estimation processes. Because
of the complicated nature of the sample design, sampling
variability has not been calculated for the estimates.
Instead, an indication of reliability is given by the number
of respondents to the relevant questionnaire item (shown as
the first row in each table). The reader must exercise
judgment in determining the amount of confidence to place in
an estimate.

Procedures for Using Percentage Estimates to Represent Visitors 
The International Trade Administration (ITA),
Nation Travel and Tourism Office (NTTO) has weighted the
Survey of International Air Travelers (SIAT) results to the DHS I92/APIS passenger totals for
U.S. residents traveling from the U.S. to other countries. Because this report presents weighted results, the
percentage estimates found in the report can be expanded to
estimate the total population of U.S. visitors to an
international destination.

Start with the overall population estimate or control total for
the column of interest. To illustrate an example, start with
Column #1, typically the primary column in a custom report
that defines the data subset for the report. The population
estimate or control
total for Column #1 is found in the last row in Table 1 in
the first column.

To further the example, consider how you
would calculate a volume estimate for those travelers
indicating that their main purpose of trip was convention or
conference. Use the control total for Column #1 and multiply
by the cell percentage found under that column in Table 14,
"Q13a. What is the main purpose of your trip?," Row #2 for
convention or conference visitors.

Always round the calculated volume
estimate to the nearest thousand; the survey estimates are
not precise enough to accurately estimate the last three
digits. Also, remember to use the correct population control
total from the corresponding column for the cell of
interest. This process can be used with any of the
percentages found within tables and is facilitated by
receiving the Excel format of the report.

Sample Size and Accuracy of the Estimates 
In of 2006 the NTTO
implemented a new policy with regard to releasing visitor
estimates based upon smaller sample sizes. If the number of
sampled visitors to a particular destination is under 400,
the NTTO will not calculate or provide an estimate of the total
number of visitors to the destination even though an
estimate could be developed. Additionally, the NTTO strongly
suggests that all users of these statistics do not attempt to
calculate visitor estimates when it appears that the sample
size is less than 400. The next paragraph contains an
explanation of how to determine when a cell may have a
sample that is too small to calculate an estimate.

A guideline
has been developed for estimating the number of respondents
in a cell. By using the first row in a table, the number of
respondents, you can estimate the unweighted number in the
cell. Divide the number of respondents in the column in
question by 100. For example, what is a lowest percentage
that should be used for estimating visitor volumes in a
custom report showing a respondent value of 5,730 for the
column? Divide 400 by 5,730 with a result of .0698 or 7.0%.
Looking down the column with 5,730 respondents at the top,
any cell with a value 7.0% or more probably^{1}
has a sample size of 400 or greater and can be used to
create an estimate for that cell. Cells with less than 7.0%
probably have sample sizes under 400 and should not be used
to assess visitor characteristics.

If you have any questions regarding the
logic of the process, or how to obtain the visitor estimates
for other segments, please call the ITA, National Travel and
Tourism Office, at (202) 4824029. Any staff member can
answer your "how to" questions. Mr. Richard Champley is the
program manager for the SIAT Survey. 
More
detailed questions relating to the survey results should be
directed to Mr. Champley. For additional written information, click here. 
^{1} Because the data are weighted, this mathematical procedure gives
estimates of sample sizes, not exact sample sizes. 