THE NON-ECONOMETRICIAN'S LAMENT As soon as I could safely toddle My parents handed me a Model; My brisk and energetic pater Provided the accelerator. My mother, with her kindly gumption, The function guiding my consumption; And every week I had from her A lovely new parameter, With lots of little leads and lags In pretty parabolic bags. With optimistic expectations I started on my explorations, And swore to move without a swerve Along my sinusoidal curve. Alas!  I knew how it would end: I've mixed the cycle with the trend, And fear that, growing daily skinnier, I have at length become non-linear. I wander glumly round the house As though I were exogenous, And hardly capable of feeling The difference 'tween floor and ceiling. I scarcely now, a pallid ghost, Can tell ex ante from ex post: My thoughts are sadly inelastic, My acts invariably stochastic. -- Sir Dennis H. Robertson