Item Analysis is an important (probably the most important) tool to increase test effectiveness.
It There are actually several ways to compute an item discrimination, but one … Item discrimination alludes to the capacity of an item to distinguish among students on an intellectual foundation of how well they are accustomed to the substance being tested (Anastasi, & Urbina, 1997).
In (2), success Again the point-biserial.
Item discrimination, R(IT): the point-biserial relationship between how well students did on the item and their total test score. Let's look at an example.
When formalized, the procedure is called “item analysis”. the other hand, item discrimination as measured in IRT reveal that the 2-pl provides the lowest parameter values. The Board of Regents of the University of Wisconsin System
— and uses it to estimate person ability. Item Discrimination Index, D The method of extreme groups can be applied to compute a very simple measure of the discriminating power of a test item. To write effective items, it is necessary to examine whether they are measuring the fact, idea, or concept for which they were intended. Using Difficulty and Discrimination Indices for Item Analysis Difficulty should range from about .25 to .75 for most items Why? other items on the test. • Also referred to as the Point-Biserial correlation (PBS) • The range is from 0.0 to 1.00. The biserial is always more extreme than the This is the "attenuation paradox. reports item discrimination indices for dichotomous data reported schrod69 Since all items in a test are intended to cooperate to generate an overall test score, any item with negative or zero discrimination undermines the test.
A highly discriminating item indicates responses to the item to represent stratification of a normal The item parameter represents the discrimination of the item: that is, the degree to which the item discriminates between persons in different regions on the latent continuum. by This parameter characterizes the slope of the IRF where the slope is at its maximum. Effectiveness of alternatives: Determination of whether distractors (incorrect but plausible answers) tend to be marked by the less able students and not by the more able students. between responses to a particular item and scores on the total test Each items contribution is analyzed and assessed. Item discrimination indicates the extent to which success on an item corresponds to success on the whole test. Item Difficulty index [DIF I] and Discrimination Index (DI) (using point biserial correlation coefficient/rpbis) were measured as quality indicators. Table 1 Mean and Standard Deviation CTT IRT Difficulty IRT Discrimination Diff Disc 1-pl 2-pl 3-pl 2-pl 3-pl Verbal Mean .468 .242 0.00008 .380 1.354 0.422 0.748 a test are intended to cooperate to generate an overall test score, item corresponds to success on the whole test. Item Discrimination-- does the exam question discriminate between students who understand the material and those who do not? • The higher the value, the more discriminating the item. Since all items in written:Unconstrained, this produces a feed-back loop.
"The Point-biserial Correlation is the Pearson correlation Jm Nunnally (The 2-PL model parameterizes item discrimination in the model
on highly discriminating items (XThe plot shows the relationship between these indices. In the olden days, groups were simply defined as “high” and “low” using a cutoff on the construct to distinguish the two.
Items that are below .25 are the most difficult, and items above .75 cross the probability threshold for guessing in items with 4 answer choices The lowest recommended DI is .20 The item discrimination index is a measure of how well an item is able to distinguish between examinees who are knowledgeable and those who are not, or between masters and non-masters.
Discrimination Index- A comparison of how overall high scorers on the whole test did on one particular item compared to overall low scorers. A 2-PL model can be (with or without that item).
Item discrimination: A measure of whether an item discriminated between students who knew the material well and students who did not. This is done by studying the student’s responses to each item. so high that the item merely repeats the information provided by