A frequent but often conveniently ignored problem in experimentation involving longitudinal and cross-sectional data is heterogeneity in variances across experimental units. Under such conditions conventional and popular OLS methods often perform poorly, producing biased results. Motivated by a...

In increasingly competitive and deregulated service environments, telecommunications service providers are interested in using advertising to stimulate usage. Measuring response in telephone usage to advertising presents difficulties because the effects are likely to be small, and the usage...

For experience goods, such as motion pictures, consumers rely on third-party endorsements as quality signals. Often, other media are used to disseminate such endorsements. As a result, their impact on a consumer is likely to depend on the consumer's type and frequency of media choices—that is,...