Sort the data and inspect extreme values
Use the IQR rule: values below Q1 – 1.5×IQR or above Q3 + 1.5×IQR
Use z-scores: values with |z| > 3 are often outliers
Use box plots to visually spot points beyond whiskers
Use scatter plots to identify isolated points
Use histograms to find unusually distant values
Use the modified z-score with median and MAD
Check residuals in regression models for unusual points
Compare values against domain-specific thresholds
Validate suspicious points against data entry or measurement errors