Sampling methods: (1) Random sampling: Each unit has equal probability; (2) Systematic: Every kth unit; (3) Stratified: Divide into strata, sample from each; (4) Cluster: Divide into clusters, randomly select clusters; (5) Quota: Meet specific quotas by category; (6) Judgmental: Expert selection. Random sampling advantages: Unbiased, representative. Systematic: Practical, efficient. Stratified: Ensures representation of subgroups. Example: Population 1000 students, need 100. Random: Assign numbers 1-1000, pick 100 randomly. Stratified: 600 science, 400 arts. Sample 60 science, 40 arts. Solving: Identify population structure. Choose appropriate method. Execute sampling plan. Exam tip: Match method to research question. Understand bias sources. Practice: Various sampling scenarios.