A discussion on disease severity index values. Part II: using the disease severity index for null hypothesis testing

The objective of this work is to explore the effects on both of different scales (i.e. those having equal or unequal classes, or different widths of intervals) and of the selection of values for scale intervals (i.e. the ordinal grade for the category or the midpoint value of the interval) on the null hypothesis test for the treatment comparison. A two‐stage simulation approach was employed to approximate the real mechanisms governing the disease‐severity sampling design. Subsequently, a meta‐analysis was performed to compare the effects of two treatments, which demonstrated that using quantitative ordinal rating grades or the midpoint conversion for the ranges of disease severity yielded very comparable results with respect to the power of hypothesis testing. However, the principal factor determining the power of the hypothesis test is the nature of the intervals, not the selection of values for ordinal scale intervals (i.e. not the mid‐point or ordinal grade). Although using the percent scale is always preferable, the results of this study provide a framework for developing improved research methods where the use of ordinal scales in conjunction with a DSI is either preferred or a necessity for comparing disease severities.

Overview of the options for assessing disease severity, and specifically the process used for establishing a quantitative ordinal scale using a DSI regarding the number of grades, the nature of the grade values and the method (interval midpoint ...

Source: Annals of Applied Biology - October 18, 2017 Category: Biology Authors: K.S. Chiang, H.I. Liu, J.W. Tsai, J.R. Tsai, C.H. Bock Tags: RESEARCH ARTICLE Source Type: research