observational study

1.Bias is one of the main concerns to ensure validity and reliability of research. Discuss with specific example on type of bias (1000 words)
2.Dr. Cindy would like to conduct an observational study to identify facial expression during deception. By using a specific example, explain the concept of
a) Cross-sectional studies (300 words)
b) Cohort study (300 words)
c) Case-control study (400words)