diff --git a/NEED/README.md b/NEED/README.md
index 8678883c0d4efefbdce21df22cc7f6b0357b44aa..f984d087e223e933108bb0f66f8330f913e28037 100644
--- a/NEED/README.md
+++ b/NEED/README.md
@@ -13,7 +13,7 @@ Notes (mostly to self):
 * The End User License file (EULF) dataset is a sample of just over 4 million households 
 * EULF is a semi-random sample of the 8m records which have an Energy Performance Certificate. 
  * It includes only those with valid values on key variables (Property Age, Property Type, Floor Area Band and Energy Efficiency Band) and (especially) valid observations for electricity in 2012. 
- * Records were selected based on the frequency of household type in the dataset relative to the total dwelling stock so that uncommon property types are over-represented, common types are under-represented and the supplied weight corrects for this. 
+ * Records were selected based on the frequency of household type in the dataset relative to the total dwelling stock so that uncommon property types (e.g. older detached properties) are over-represented and common types (e.g. flats where turnover is high) are under-represented. The supplied weight corrects for this for descriptive analaysis. 
  * Implications for sample bias unclear - there may be other systematic biases not captured by the weight?
 * UPRN = unique property reference = linkage mechanism (uses AddressBase)
 * Bias caused by linkage failure is unknown although the DECC NEED Data Framework report from 2011 suggest match rates of 94%-100% (https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/209264/Annex_B_-_Quality_Assurance.pdf)