Abbreviated Interrupted Time-Series - Institute for Policy Research

Concerns with Contrast 1
• Possible low power due to low number of groups (3:
public, Catholic, non‐Catholic private) with 8 time
points
– So only 24 degrees of freedom
• Catholic sex abuse scandals in 2002 result in parents
taking their children out of Catholic schools
• No evidence that
– school leavers caused a drop in average student
achievement in Catholic schools or
– public and other private school effects are due to
transfers from Catholic schools
• Data from other private schools provides a
unconfounded replicate, but never stat sig.