114 research outputs found
Reproducibility of the mfERG between instruments
Purpose First, to examine both the reproducibility of the multifocal electroretinogram (mfERG) recorded on different versions of the same instrument, and the repeatability of the mfERG recorded on a single instrument using two different amplifiers. Second, to demonstrate a means by which multicenter and longitudinal studies that use more than one recording instrument can compare and combine data effectively. Methods Three different amplifiers and two mfERG setups, one using VERISā¢ 4.3 software (mfERG1) and another using VERISā¢ Pro 5.2 software (mfERG2), were evaluated. A total of 73 subjects with normal vision were tested in three groups. Group 1 (nĀ =Ā 42) was recorded using two amplifiers in parallel on mfERG1. Group 2 (nĀ =Ā 52) was recorded on mfERG2 using a single amplifier. Group 3 was a subgroup of 21 subjects from groups 1 and 2 that were tested sequentially on both instruments. A fourth group of 26 subjects with diabetes were also recorded using the two parallel amplifiers on mfERG1. P1 implicit times and N1-P1 amplitudes of the 103 local first order mfERGs were measured, and the differences between the instruments and amplifiers were evaluated as raw scores and Z-scores based on normative data. Measurements of individual responses and measurements averaged over the 103 responses were analyzed. Results Simultaneous recordings made on mfERG1 with the two different amplifiers showed differences in implicit times but similar amplitudes. There was a mean implicit time difference of 2.5Ā ms between the amplifiers but conversion to Z-scores improved their agreement. Recordings made on different days with the two instruments produced similar but more variable results, with amplitudes differing between them more than implicit times. For local response implicit times, the 95% confidence interval of the difference between instruments was approximately Ā±1 Z-score (Ā±0.9Ā ms) in either direction. For local response amplitude, it was approximately Ā±1.6 Z-scores (Ā±0.3Ā Ī¼V). Conclusions Different amplifiers can yield quite different mfERG P1 implicit times, even with identical band-pass settings. However, the reproducibility of mfERG Z-scores across recording instrumentation is relatively high. Comparison of data across systems and laboratories, necessary for multicenter or longitudinal investigations, is facilitated if raw data are converted into Z-scores based on normative data
School Vouchers and Student Achievement: Recent Evidence, Remaining Questions
In this article, we review the empirical evidence on the impact of education vouchers on student
achievement, and briefly discuss the evidence from other forms of school choice. The best
research to date finds relatively small achievement gains for students offered education vouchers,
most of which are not statistically different from zero. Further, what little evidence exists
regarding the potential for public schools to respond to increased competitive pressure generated
by vouchers suggests that one should remain wary that large improvements would result from a
more comprehensive voucher system. The evidence from other forms of school choice is also
consistent with this conclusion. Many questions remain unanswered, however, including
whether vouchers have longer-run impacts on outcomes such as graduation rates, college
enrollment, or even future wages, and whether vouchers might nevertheless provide a costneutral
alternative to our current system of public education provision at the elementary and
secondary school level
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