Fix response rates for small schools by accounting for expected minimum counts of responses less than 10

app/models/student_response_rate_calculator.rb

@@ -28,11 +28,14 @@ class StudentResponseRateCalculator < ResponseRateCalculator
   end
 
   def survey_items_with_sufficient_responses(grade:)
+    threshold = 10
+    quarter_of_grade = enrollment_by_grade[grade] / 4
+    threshold = threshold > quarter_of_grade ? quarter_of_grade : threshold
     SurveyItem.joins('inner join survey_item_responses on  survey_item_responses.survey_item_id = survey_items.id')
               .student_survey_items
               .where("survey_item_responses.school": school, "survey_item_responses.academic_year": academic_year, "survey_item_responses.grade": grade, "survey_item_responses.survey_item_id": subcategory.survey_items.student_survey_items)
               .group('survey_items.id')
-              .having('count(*) >= 10')
+              .having("count(*) >= #{threshold}")
               .count
   end
 

spec/models/response_rate_calculator_spec.rb

@@ -65,8 +65,9 @@ describe ResponseRateCalculator, type: :model do
 
         context 'there are responses for another survey item but not enough to meet the minimum threshold' do
           before do
-            create_list(:survey_item_response, 9, survey_item: insufficient_student_survey_item_1, academic_year:,
-                                                  school:, grade: 1)
+            less_than_a_quarter_of_respondents_for_first_grade = 4
+            create_list(:survey_item_response, less_than_a_quarter_of_respondents_for_first_grade, survey_item: insufficient_student_survey_item_1, academic_year:,
+                                                                                                   school:, grade: 1)
           end
           it 'returns an average of the response rates for all grades' do
             expect(StudentResponseRateCalculator.new(subcategory:, school:, academic_year:).rate).to eq 50