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This study explores different methods for estimating total error in student loan audit data and suggests improvements for better accuracy and efficiency.
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Standard errors from audits Sumit Rahman, Department for Business, Energy and Industrial Strategy
Student Loans Company (England) • 4 types of loan (tuition fee loans, maintenance loans, maintenance grants, part-time grants), and two different academic years falling in the same financial year – so 8 strata • Simple random sample of loans from each stratum (different sampling rates) • Administrative data with no non-response
Estimating total error Step 1: estimate the stratum error rate
Estimating total error Step 2: estimate the stratum error total
Estimating total error Step 3: estimate the error total Step 4 (optional): estimate the overall error rate
Estimating total error In one step
Estimating total error In one step Step 1: estimate the stratum error rate
Estimating total error In one step Step 1: estimate the stratum error rate Step 2: estimate the stratum error total
Estimating total error In one step Step 3: estimate the error total Step 1: estimate the stratum error rate Step 2: estimate the stratum error total
Estimating total error In one step
Estimating total error In one step
Standard errors • So our estimate of total error was £115m • And the standard error estimate is £31m • That’s really high – the coefficient of variation is 27% • A 95% confidence interval is £115m +/- £61m • Or £115m +/- 53%
Skills Funding Agency (England) Separate ratio census
Estimating the total error Step 1: estimate the college error rate
Estimating the total error Step 2: estimate the stratum error rate
Estimating the total error Step 3: estimate the stratum error total
Estimating the total error Step 4: estimate the error total Step 5 (optional): estimate the overall error rate
Estimating the total error In one step Step 1: college error rate
Estimating the total error In one step Step 1: college error rate Step 2: stratum error rate
Estimating the total error In one step Step 1: college error rate Step 2: stratum error rate Step 3: stratum error total
Estimating the total error In one step Step 1: college error rate Step 4: error total Step 2: stratum error rate Step 3: stratum error total
Improvements to consider • Didn’t make use of ratio residuals. After the transformation I used the default formulas for the standard error in a clustered design – but using expansion residuals • In this set-up, PPS sampling is sensible. We could probably do this using funding as our measure of size rather than number of colleges in a stratum and number of learners in a college • Model based estimation?