How do you estimate an effect with difference-in-differences?
Difference-in-differences compares change in a treated group with change in an untreated group. Identification relies on credible parallel trends without treatment.
Direct answer
Estimate an ATT for groups and periods covered by the design.
Difference-in-differences compares change in a treated group with change in an untreated group. Identification relies on credible parallel trends without treatment.
DiD = (ȲT,post−ȲT,pre) − (ȲC,post−ȲC,pre)ESTIMAND
Estimation profile
- Unit of analysis
- Assigned unit × group × periodControlled scientific terminology
unit × group × period - Exact estimand
ATT in a two-group, two-period design- Model or deliverable
DiD = (ȲT,post−ȲT,pre) − (ȲC,post−ȲC,pre)
01—08
Verifiable analysis framework
- 01Question
How do you estimate an effect with difference-in-differences?
- 02Estimand
ATT in a two-group, two-period design · unit × group × period
- 03Data
unit_id · group · period · treatment_start · outcome
- 04Model or deliverable
DiD = (ȲT,post−ȲT,pre) − (ȲC,post−ȲC,pre)
- 05Declared calculation
DiD = (ȲT,post−ȲT,pre) − (ȲC,post−ȲC,pre) → ATT in a two-group, two-period design
- 06Uncertainty checks
Pre-trends · Anticipation · Use group-time ATT for staggered adoption · Clustered uncertainty
- 07Method-specific validation
Check data, estimate stability and interpretation limits. Pre-trends · Anticipation · Use group-time ATT for staggered adoption · Clustered uncertainty
- 08Limitations
Prove future parallel trends from pre-period data alone.
Required variables
unit_idgroupperiodtreatment_startoutcome
Checks · Controlled scientific terminology
- Pre-trends
- Anticipation
- Use group-time ATT for staggered adoption
- Clustered uncertainty
Estimate an ATT for groups and periods covered by the design.
Prove future parallel trends from pre-period data alone.
Scientific sources
2 sources
Dataset · Tool
Method connections
