Selection Bias
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Selection Bias

The survey results showing the positive influence of The Anne Samson Jerusalem Journey (TJJ) trips to Israel
(“Orthodox Israel Trips Keeping Young Jews Engaged,” May 15) may suffer from
a selection bias that undermines the validity of the conclusions. Students
who choose to go on these trips are likely to be more engaged and committed
Jews to begin with, which is why they choose the TJJ trip, and thus it is not
the trip itself that is responsible for their responses.

The only way to
ensure the validity of the conclusions is to either control for one’s
pre-trip commitment (by having the students fill out a pre-trip survey), or
to randomly assign students to different types of trips. Absent these
methods, we can’t be confident in the study’s conclusions.

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