Tim Cejka

Economics PhD Student at UC Berkeley

About me




Contact me by email or follow me on my social networks:

Working papers and ongoing projects:

Long-Run Impacts of In-Utero Ramadan Exposure: Evidence from Administrative Tax Records with Mazhar Waseem
Last draft , VoxEU Column , Vox Webcast

Using Ramadan fasting as a natural experiment, we estimate the long-run impacts of in-utero health and nutrition shocks on adult outcomes. We exploit administrative tax return data comprising the universe of income tax returns filed in Pakistan during 2007–2009. The data allow us to link in-utero Ramadan exposure of individuals with their later life labor market outcomes. We find a robust negative effect of Ramadan exposure on earnings (a lower-bound estimate of around 2–3 percent). The exposed individuals are less likely to be in high-skilled occupations and less likely to be in the top of the income distribution. Using nationally representative survey data we show that our results are unlikely to be driven by selective timing of conception.

Heterogeneous Welfare Effects of Corrective Taxes: Evidence from South Africa’s Soda Tax with Marlies Piek and Mazhar Waseem

Sin taxes are increasingly being used to discourage the consumption of internalityproducing goods. A major concern with sin taxes is that they are regressive. But the behavioral biases they seek to correct may also be concentrated among the poor. The welfare consequences of sin taxes are therefore not clear, depending inter alia on the distribution of the demand elasticity and behavioral bias in the population. In this project, we intend to exploit the introduction of South Africa’s Health Promotion Levy to estimate the extent and distribution of welfare gains created by a representative sin tax. We will extend the framework of Allcott et al. (2019) to allow imperfect pass-through of the levy, following O’Connell & Smith (2021). Combining administrative data from CIT, VAT, and Customs records with survey data and using event-study and difference-in-differences research designs we will then estimate the parameters required to assess how the levy affected the welfare of the poor and rich in South Africa.

Reflexivity of Predictions as a Statistical Bias
Last draft

It has been argued that reflexive predictions pose a methodological problem to the social sciences by jeopardizing objective theory testing. This problem apparently arises from a reflexive prediction’s ability to modify the evidential import conferred by an observation upon a tested theory. As a classic example, reflexive predictions can lead to a spurious confirmation of a theory (Merton, 1949). In a recent article, Kopec has argued that spurious confirmations constitute just one of multiple undesirable consequences of reflexive predictions, which he argues include both overstating and understating an observation’s evidential support as well as mistaking counter-evidence for evidence (Kopec, 2011). I agree that reflexive predictions may alter the evidential import of an observation; however, I will argue that this is not a genuinely methodological problem for social science but instead a technical one. Specifically, I will show that the reflexivity of a prediction is merely a type of statistical bias and, as such, can be dealt with using standard econometric methods. After developing a new definition of reflexive predictions, I will show that econometric methods can in principle eliminate reflexivity from the predictions used to test theories in social science.