Volume 21, Issue 2 (1992)
Estimating Trend in Progress Monitoring Data: A Comparison of Simple Line-Fitting Methods
Richard Parker, Gerald Tindal, Stephanie Stein
Four simple line-fitting procedures are presented for practitioners to quickly summarize student time series performance data. Two are in common use - Koenig’s “quarter-intersect” and White’s “split-middle” adjustment, while two - Tukey I and Tukey II - are less known. Each of the four can be performed on a medium-size classroom dataset in less than 3 minutes. The four procedures were assayed against three criteria: (a) matching line slopes to an ordinary least squares (OLS) standard; (b) “best fit” to the data (minimizing residuals); and (c) prediction of a future reading score at Week 16. Weekly oral reading fluency data were collected on 45 Grade 4 and 5 students with reading disabilities, over a period of 12 weeks. Tukey I and II techniques generally outperformed the Koenig and White line-fitting methods, especially White’s “split-middle” adjustment. Performance differences were generally large enough to be educationally meaningful. Given the small database supporting the popular White and Koenig procedures, the authors recommend that practitioners cautiously try out Tukey I and II procedures, comparing results with Koenig’s and White’s procedures. Of course, further psychometric studies of all four procedures are needed also. The authors discuss three notable study limitations: limited generalizability, use of the future score prediction criterion, and no instructional use of the best fit lines.
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