- [Narrator] The path from cause
to effect is dark and dangerous.
But the weapons
of Econometrics are strong.
[Attack] with fierce
and flexible instrumental variables
when nature blesses you
with fortuitous random assignment.
[gong rings]
Randomized trials are the surest
path to ceteris parabus comparisons.
Alas, this powerful tool
is often unavailable.
But sometimes, randomization
happens by accident.
That's when we turn
to instrumental variables,
IV for short.
- [Voice whispers] Instrumental
variables.
- [Narrator] Today's lesson
is the first of two on IV.
Our first IV lesson begins
with a story of schools.
- [Josh] Charter schools
are public schools
freed from daily district oversight
and teacher union contracts.
The question of whether charters
boost achievement
is one of the most important
in the history
of American education reform.