The Output tab provides the ability to tailor the output report to your specific needs.
The Output Options Tab
Item statistic flagging allows you to specify an acceptable range for a statistic. For example, if you want to identify all items that have a P (proportion correct) outside 0.40 and 0.98, it can be specified here, and then the output will label items with low P (too hard) as “LP” and high P (too easy) as “HP.” The “acceptable item mean” range is used to flag the item means of polytomous items to identify outlier items; for example if you have a rating scale of 1 to 5 you might want to flag means over 4.0 and under 2.0. These statistics and flags are further explained in later in this manual.
If you want to have the point-biserial and biserial correlations corrected for spuriousness, click the check box next to that statement. Spuriousness refers to the fact that an item’s scores are included in the total score, so correlating an item with the total score implies that it is being correlated with itself to some extent. This effect is negligible if there are a large number of items on the test (e.g., more than 30), but Iteman provides the option to correct for this issue, which should be utilized for tests of 30 items or less. You can use it for all tests if you prefer.
Selecting the “Consider skip as incorrect option” box will mean that skip/omit will then have the full complement of option statistics computed for them, essentially treating a 4 option MC item as 5 options. It also scores such responses as Incorrect, and scoring omits as incorrect affects the reliability coefficients. For polytomous items, omits are automatically excluded from the option statistics.
Groups for quantiles allows you to increase or decrease the number X of examinee groups used for constructing the quantile plots. This number can range from 2 to 7. Larger numbers of points are recommended only for large sample sizes of at least 1,000 examinees.
Differential Item Functioning (DIF)
DIF is an analysis of bias, for example if the item is easier for an ethnic majority, using the Mantel-Haenszel approach. To request a DIF analysis for each scored dichotomous item select the checkbox next to that option.
- Specify the characters used to identify the reference and focal groups. These characters are not case sensitive. You can only compare 2 groups at once, so if you have a majority group and 3 minorities, you will have to run DIF 3 separate times.
- The “Ability groupints for DIF” option specifies the number of ability levels created for purposes of the Mantel-Haenszel DIF test.