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Subject: statfit + снова ретинограф Hood and Li demonstrated that local M-ERG responses from patients with retinitis pigmentosa are more accurately fit by normal templates that are multiplicatively scaled over time (rather than additively scaled). Multiplicative scaling stretches the entire normal response along the time axis, whereas additive scaling shifts the normal response by addition of a simple latency delay. Preliminary analyses of our data showed that multiplicative time scaling provided superior fits to local ERGs in diabetic eyes as well. For short implicit time delays (<2 msec), quantitative goodness-of-fit measures indicated that the two methods were comparable. (The goodness-of-fit measure provided by this program is the "statfit" value that is the least-squares statistic minimized during the fitting routine; a statfit of 0.0 indicates a perfect fit, and a statfit of 1.0 indicates that the fitted template does no better than the mean of the data). For responses with longer delays, however, additive scaling produced much larger (poorer) statfit values (e.g., ~0.45 versus ~0.25, using the multiplicative method). Therefore, all fits were performed using multiplicative scaling. The mean (±SD) statfit value for all patient local ERG fits was 0.27 ± 0.09, and the range was 0.07 to 0.68, indicating that the template fits were accurate. In fact, the residual error of the fit was typically caused by mismatch of the late components (50 to 80 msec); reanalysis of a subset of responses with high statfit values (i.e., >0.5) using only the first 50 msec of these responses, revealed no differences for derived implicit times or amplitudes.Что эт за звери такие ''statfit'' и ''SD''? Подскажите, т.к. я теряюсь в догадках.. Спасибо.. |
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