mode = most common value (think: hip, popular, fashionable)

• computing mode with graphical techniques

median = middle value (think: median of a street)
 
 
 

mean = balancing point in histogram

• best guess of a value if no other information about distribution
• what people commonly refer to as the average

sensitivity to outliers
 
 
 
 

percentile - value at or below which a specific percentage of distribution falls
 
 

quartile - value at below which 25% (lower; Q1), 50% (median), or 75% (upper; Q3) of distribution falls
 
 
 
 

Distribution Shapes
 

unimodal
 

bi/multimodal
 

symmetrical

• uniform (special case) = all values have same number of observations

positively skewed (skewed to right)
 
 

negatively skewed (skewed to left)