add rasch functionality to form generation

app/lib/irt/item_information_function.py

@@ -1,6 +1,7 @@
 import logging
 
 from lib.irt.models.three_parameter_logistic import ThreeParameterLogistic
+from lib.irt.models.rasch import Rasch
 from lib.errors.item_generation_error import ItemGenerationError
 
 
@@ -20,6 +21,10 @@ class ItemInformationFunction():
                 return (self.model_data.a_param * q *
                         (p - self.model_data.c_param)**2) / (p * (
                             (1 - self.model_data.c_param)**2))
+            elif self.model_data.model == 'RASCH':
+                p = Rasch(self.model_data, kwargs).result()
+                q = 1 - p
+                return p * q
             else:
                 # potentially error out
                 raise ItemGenerationError(

app/lib/irt/item_response_function.py

@@ -1,4 +1,5 @@
 from lib.irt.models.three_parameter_logistic import ThreeParameterLogistic
+from lib.irt.models.rasch import Rasch
 from lib.errors.item_generation_error import ItemGenerationError
 
 
@@ -10,5 +11,7 @@ class ItemResponseFunction():
     def calculate(self, **kwargs):
         if self.model_data.model == '3PL':
             return ThreeParameterLogistic(self.model_data, kwargs).result()
+        elif self.model_data.model == 'RASCH':
+            return Rasch(self.model_data, kwargs).result()
         else:
             raise ItemGenerationError("irt model not supported or provided")

app/lib/irt/models/rasch.py

@@ -5,7 +5,7 @@ from lib.irt.models.base import *
 class Rasch(Base):
 
   def result(self):
-    return 0.0
+    return (1 / (1 + self.e(-1 * (self.theta - self.b_param))))
 
   @classmethod
   def ability_estimate(self, items) -> float: