We consider estimation and inference for a regression coefficient in panels with interactive fixed effects (i.e., with a factor structure). We show that previously developed estimators and confidence intervals (CIs) might be heavily biased and size-distorted when some of the factors are weak. We...

The paper addresses the question whether current tariffs for telecommunications services provided by the Swedish telecommunications company, Televerket (TVT), are optimal, second-best 'Ramsey' prices. Focusing on two tariffs for telecommunications services those on subscription and calling time...