“Households with maids use 20 per cent more water”: Correlation is not causation

Careful reporting of survey findings is important. Focusing disproportionately on the observation that households with foreign domestic workers use 20 per cent more water than those without (ST, Mar. 9) – 160 litres compared to 135 litres, on a daily, per-capita basis – and attributing the higher water consumption to the hypothesis that “washing and cooking activities are done more often in homes with maids” results in two problems. First, the conflation of correlation and causation, especially when other factors potentially related to consumption, besides the number of individuals in a household, have not been adequately considered; and second, relatedly, the leap to a causal explanation without convincing empirical evidence.