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Field
Last Published
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Before
July 29, 2020 01:02 PM
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After
August 10, 2020 11:17 AM
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Field
Primary Outcomes (End Points)
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Before
Credit card balance or indicator for repaid more than the pre-intervention 3-month average. (Determination made after power calculations.)
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After
Credit card repayment amount
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Field
Power calculation: Minimum Detectable Effect Size for Main Outcomes
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Before
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After
We conducted power analysis to determine minimum detectable effects (MDEs) with α=0.05 and power of 1-β=0.80. We assume the control group sample size is 41,776 and the treatment group is 83,552, pooling together treatment 1 and 2. We run a two-tailed comparison of means, assuming control and treatment groups have the same standard deviations.
Based on the analysis, the minimum detectable effect size of credit card repayment amount is $39 on a base of $1,361, or 3% of the mean, and standard deviation of $2,312. Section 4.3 of the pre-analysis plan describes the power analysis in further detail, and table 1 of the pre-analysis plan reports the minimum effect sizes for primary and secondary outcomes. We note when we account for multiple testing, adjusted p-values for a given effect size are roughly twice as large as unadjusted p-values. Any adjustments are made within outcome variable domains (outlined in section 3.3).
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Field
Secondary Outcomes (End Points)
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Before
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After
1. Engagement domain:
a. Indicator for saw T1
b. Indicator for interacted with T1
c. Indicator for saw T2
d. Indicator for interacted with T2
2. Credit card repayment domain:
a. Indictor for repaid more than pre-intervention 3-month average
b. Indicator for repaid more than minimum due
c. Indicator for repaid the full amount due
3. Credit card borrowing domain
a. Revolving balance
b. Indicator for balance higher than pre-intervention 3-month average
c. Interest charges
4. Savings domain
a. Savings balance
b. Indicator for balance higher than pre-intervention 3-month average
c. Interest earnings
5. Net financial benefit domain
a. Net interest (savings interest earnings – credit card interest charges)
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