Q1: I am not familiar with "percentage of total information" - do you have a reference?
Q2: When you are looking at the information plot, you can pull down the plot menu and at the bottom you find the option "Save plot data". There you will the information value for each x-axis value, from which you can calculate the SE.
Q1. I apologize for "percentage of total information." My question is about "amount of total information"
The reference is "Item response theory and the measurement of clinical change". Reise SP, Havil MG.2005. Journal of Personality Assessment.Jun;84(3):228-38.
They report the test reliability in IRT as below. The lower line corresponsd(approximately) to a reliability coefficient of 0.90(SE=.316), and the upper line corresponds to a reliability coefficient of 0.95(SE=.223).
1. How to calcurate a reliability in IRT?
2. Is there way to calcurate amount of test information in the range -3< Theta <3 ?
1. No - because the formula does not involve model parameters (otherwise Model Constraint could be used).
2. Here is how you do it in Mplus.
Use the plot menu's "View plots" and choose "Total information curve (TIC) for all items". Then go back to the plot menu and click on "Save plot data". That saved data then contains the information value for every x-axis (theta) value. You can then find SE(theta-hat) as the inverse square root of the information value and any x-axis point (like in that IRT article). And then you can get reliability from that - using the formula and e.g. Excel or R.