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Randomization in Practice

Randomization in Practice. Unit of randomization. Randomizing at the individual level Randomizing at the group level School Community / village Health center District How do you tell which level to randomize at?. Unit of randomization.

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Randomization in Practice

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  1. Randomization in Practice

  2. Unit of randomization • Randomizing at the individual level • Randomizing at the group level • School • Community / village • Health center • District • How do you tell which level to randomize at?

  3. Unit of randomization • Individual randomization gives you a bigger sample size at lower cost • Politically may be difficult to have unequal treatment within a community • Program can only be implemented at a certain level • Spillovers

  4. How to randomize? • The lottery • Phase-in design • Rotation design • Encouragement design NB: These are not mutually exclusive

  5. How to randomize? • Simple case: the lottery • There is oversubscription: you have to choose who will benefit from the program. • Instead of choosing the beneficiaries on criteria (proximity, need), you choose them randomly • Is it fair to allocate the program randomly? • Partial lottery • Pilot before full-scale implementation

  6. How to randomize? • Phase-in design: takes advantage of expansion • You may serve everybody, but not all at once • Choose the first people served randomly • The others will be the comparison, until they get served Adapted from How to Randomize, Rachel Glennerster, J-PAL.

  7. Phase-in Design Adapted from How to Randomize, Rachel Glennerster, J-PAL.

  8. How to randomize? • Rotation design • You may serve half of the people, but don’t want to leave people out • Group A gets the program on Year 1, Group B on Year 2 • Group B is control in Year 1, Group B in Year 2

  9. Rotation design Adapted from How to Randomize, Rachel Glennerster, J-PAL.

  10. How to randomize? • Encouragement design: What to do when you can’t randomize access • Sometimes practically or ethically impossible to randomize program access • But most programs have less than 100% take up • Randomize encouragement to receive treatment Adapted from How to Randomize, Rachel Glennerster, J-PAL.

  11. Encouragement Design Adapted from How to Randomize, Rachel Glennerster, J-PAL.

  12. Key steps in conducting an experiment • Understand the program in depth (Theory of Change) • Design the study carefully • Randomly assign people to treatment or control • Collect baseline data (→ panel) • Verify that assignment looks random (← small sample) • Monitor process so that integrity of experiment is not compromised

  13. Key steps in conducting an experiment (cont.) • Collect follow-up data for both the treatment and control groups in identical ways. • Estimate program impacts by comparing mean outcomes of treatment group vs. mean outcomes of control group. • Assess whether program impacts are statistically significant and practically significant.

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