Marxism is often criticised for its 'outdated economics' which wrongly downplays the state's role in modern social life. This study uses readily available official statistics to test the validity of this critique. Although simple accounting principles are used, factory production data for 1923-70 is rigorously and systematically re-aggregated to approximate constant (fixed and circulating) and variable capital, manufacturers' surplus-value, capital composition, and rates of accumulation, exploitation and profit. A separate volume details all statistical operations and tabulates results. Capital accumulation is used to fix the curve of capitalist development and the interrelations between valueratios are used to explain the curve's shape. Conventional theories are also called on to explain trends in national income and factory production input/output series. Main conclusions drawn are that (1) marxism is empirically well-corroborated and (2) no consistent correlation holds between state intervention and economic growth. Marxian hypotheses concerning proletarianisation, economic concentration, class struggle, etc. are also tested systematically against New Zealand data and confirmed. In this light, and as rival theories of superior verisimilitude are absent, the criticism mentioned is rejected as unwarranted. Most NZ marxian analyses focus on superstructures, lacking objective bases for problem-formulation and solution, this study offers such a basis.