# Uniqueness of OLS estimates

Wooldrige says that ‘intuitively, to estimate k+1 parameters, we need at least k+1 observations’. Why is this the case?

The $$k+1$$ parameters are $$k+1$$ unknowns. In general, you need at least $$k+1$$ equations (which are observations in the context of OLS estimation) to uniquely pin down those $$k+1$$ unknowns.
• @AliLodhi: I'm not sure what you mean by "OLS first order conditions", but I have in mind the OLS regression model $y_i=\beta_0+\beta_1x_{1i}+\cdots+\beta_k x_{ki}+\epsilon_i$, where each observation $i$ is an instantiation of this equation. – Herr K. Nov 18 '19 at 17:26