Add hierarchical structure diagram of ISCO-08 classification scheme

README.md

@@ -25,6 +25,85 @@ The hierarchical structure of the ISCO-08 classification scheme, as depicted in
 | 3-digits | Minor groups |
 | 4-digits | Unit groups |
 
+*Figure 1: Hierarchical structure of the ISCO-08 classification scheme*
+
+```mermaid
+flowchart TD
+
+    Root --- 1
+    Root --- 2
+    
+    1 --- 11
+
+    2 --- 22
+    2 --- 23
+
+    22 --- 221
+    22 --- 222
+
+    23 --- 235
+
+    221 --- 2211
+    221 --- 2212
+
+    222 --- 2221
+    222 --- 2222
+ 
+    235 --- 2351
+    235 --- 2352
+
+    classDef defaultNode fill:#ffff,stroke:#333,stroke-width:2px
+    classDef highlightNode fill:#333,stroke:#333,stroke-width:2px,color:#ffff
+
+    Root((Root Node)):::defaultNode
+
+    1(
+    Major group 1: 
+    Managers):::defaultNode
+
+    11(
+    Sub-major group 11:
+    Chief Executives, Senior Officials and Legislators):::defaultNode
+
+    2(
+    Major group 2: 
+    Professionals):::defaultNode
+
+    22(
+    Sub-major group 22:
+    Health Professionals):::defaultNode
+
+    221(Minor group 221:
+    Medical Doctors):::defaultNode
+
+    2211(Unit group 2211:
+    Generalist Medical Practitioners):::highlightNode
+
+    2212(Unit group 2212:
+    Specialist Medical Practitioners):::defaultNode
+
+    222(Minor group 222:
+    Nursing and Midwifery Professionals):::defaultNode
+
+    2221(Unit group 2221:
+    Nursing Professionals):::defaultNode
+
+    2222(Unit group 2222:
+    Midwifery Professionals):::defaultNode
+
+    23(Sub-major group 23:
+    Teaching Professionals):::defaultNode
+
+    235(Minor group 235:
+    Other Teaching Professionals):::defaultNode
+
+    2351(Unit group 2351:
+    Education Methods specialists):::defaultNode
+
+    2352(Unit group 2352:
+    Special Needs Teachers):::defaultNode
+```
+
 In this context, the hierarchical accuracy measure is specifically designed to evaluate classifications within this structured framework. It emphasizes the importance of precision in classifying occupations at the correct level of specificity:
 
 1. **Major Groups (1-digit codes):** The broadest category that encompasses a wide range of occupations grouped based on their fundamental characteristic and role in the job market. Misclassification among different Major groups implies a fundamental misunderstanding of the occupational role.