From 17579baa7e3c145ab3845268d4faa02e0bc86903 Mon Sep 17 00:00:00 2001
From: Eli <94979642+eli-miriam@users.noreply.github.com>
Date: Tue, 31 Dec 2024 15:03:29 +0000
Subject: [PATCH] ensure index date is accounted for in clinical event query
 for diabetes

---
 docs/tutorial/more-complex-transformations/index.md | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/docs/tutorial/more-complex-transformations/index.md b/docs/tutorial/more-complex-transformations/index.md
index 516446982..149b64c3a 100644
--- a/docs/tutorial/more-complex-transformations/index.md
+++ b/docs/tutorial/more-complex-transformations/index.md
@@ -175,7 +175,7 @@ There is another codelist, [`DMRES_COD`][5], that contains a single code indicat
 
 To find the patients with an unresolved diagnosis, we need to find the date of each patient's latest diabetes diagnosis event (if any) and the date of each patient's latest diabetes resolved event (if any), and take only patients where there is a diabetes diagnosis event and no subsequent diabetes resolved event.
 
-We can find the latest event for each patient matching a codelists:
+We can find the latest event before the index date for each patient matching a codelists:
 
 ```ehrql
 from ehrql import codelist_from_csv, show
@@ -189,12 +189,14 @@ resolved_codes = codelist_from_csv("codelists/nhsd-primary-care-domain-refsets-d
 last_diagnosis_date = (
     clinical_events.where(clinical_events.snomedct_code.is_in(diabetes_codes))
     .sort_by("date")
+    .where(clinical_events.date <= index_date)
     .last_for_patient()
     .date
 )
 last_resolved_date = (
     clinical_events.where(clinical_events.snomedct_code.is_in(resolved_codes))
     .sort_by("date")
+    .where(clinical_events.date <= index_date)
     .last_for_patient()
     .date
 )
@@ -225,12 +227,14 @@ resolved_codes = codelist_from_csv("codelists/nhsd-primary-care-domain-refsets-d
 last_diagnosis_date = (
     clinical_events.where(clinical_events.snomedct_code.is_in(diabetes_codes))
     .sort_by("date")
+    .where(clinical_events.date <= index_date)
     .last_for_patient()
     .date
 )
 last_resolved_date = (
     clinical_events.where(clinical_events.snomedct_code.is_in(resolved_codes))
     .sort_by("date")
+    .where(clinical_events.date <= index_date)
     .last_for_patient()
     .date
 )
@@ -272,12 +276,14 @@ is_registered = (
 last_diagnosis_date = (
     clinical_events.where(clinical_events.snomedct_code.is_in(diabetes_codes))
     .sort_by("date")
+    .where(clinical_events.date <= index_date)
     .last_for_patient()
     .date
 )
 last_resolved_date = (
     clinical_events.where(clinical_events.snomedct_code.is_in(resolved_codes))
     .sort_by("date")
+    .where(clinical_events.date <= index_date)
     .last_for_patient()
     .date
 )