Added new model

docs.md

@@ -33,7 +33,7 @@ Example models include:
 
 ### Downstream models
 
-Downstream models are fit using feature vectors (embeddings or IDPs) for all scans from the training set. For age, linear regression is used. This model is then applied to validation and testing sets to measure out-of-sample performance. For sex (genetic F/M) and clinical diagnosis (clinical Alzheimer's disease (AD)/cognitively normal(CN)), linear discriminant analysis classification is used. These models are then applied to validation and testing sets to measure out-of-sample performance.
+Downstream models are fit using feature vectors (embeddings or IDPs) for all scans from the training set. For age, linear regression is used. This model is then applied to validation and testing sets to measure out-of-sample performance. For sex (genetic F/M) and clinical diagnosis (clinical Alzheimer's disease (AD)/cognitively normal(CN)), linear discriminant analysis classification is used. These models are then applied to validation and testing sets to measure out-of-sample performance. Age and sex models are only fit and evaluated on scans from subjects with a clinical diagnosis of cognitively normal.
 
 ### Rank computation