The leverage measure threshold for identifying potentially influential observations is calculated as 3(k+1)/n, where k is the number of independent variables and n is the number of observations.

Given:

• k = 4 (independent variables)
• n = 80 (observations)

Threshold = 3(4 + 1)/80 = 3(5)/80 = 15/80 = 0.1875 ≈ 0.19

However, the question asks for the leverage measure above which an observation is considered potentially influential. The rule of thumb is that observations with leverage greater than 3(k+1)/n are considered potentially influential. Since 0.15 is the closest value below the threshold of 0.1875, and observations above this threshold are influential, the answer is 0.15.