A potential source of bias in estimating impact of televised campaign ads

One popular strategy for estimating impact of televised campaign ads is by exploiting ‘accidental spillover’ (see Huber and Arceneaux 2007). The identification strategy builds on the following facts: Ads on local television can only be targeted at the DMA level. DMAs sometimes span multiple states. Where DMAs span battleground and non-battleground states, ads targeted for residents of battleground states are… Read more →

R-Tip: Missing weights, weighted.mean

There are instances where sampling weights are not only unknown, but in fact, cannot be known (unless one makes certain unsavory assumptions). Under those circumstances, weights for certain respondents can be ‘missing’. Typically there the strategy is to code those weights as 0. However if you retain those as NA, weighted.mean etc. is wont to give you NA as an… Read more →

Sample this

What do single shot evaluations of MT (replace it with anything else) samples (vis-a-vis census figures) tell us? I am afraid very little. Inference rests upon knowledge of the data (here – respondent) generating process. Without a model of the data generating process, all such research reverts to modest tautology – sample A was closer to census figures than sample… Read more →

Moving further away from the out-party

Two things are often stated about American politics (most vociferously by Mo Fiorina): political elites are increasingly polarized, and that the issue positions of the masses haven’t budged much. Assuming such to be the case, one expects the average distance between where partisans place themselves and where they place the ‘in-party’ (or the ‘out-party’) to increase. However it appears that… Read more →

‘Representativeness heuristic’, base rates, and Bayes

From the Introduction of their edited volume: Tversky and Kahneman used the following experiment for testing ‘representativeness heuristic’ – Subjects are shown a brief personality description of several individuals, sampled at random from 100 professionals – engineers and lawyers. Subjects are asked to assess whether description is of an engineer or a lawyer. In one condition, subjects are told group… Read more →

State of the union

Over the past forty years, Proportion of Respondents Reporting At least one union member in the household has declined precipitously. (Source American National Election Studies) . Read more →

Interviewer Assesments of Respondent’s Level of Political Information

In the National Election Studies (NES), interviewers have been asked to rate respondent’s level of political information – “Respondent’s general level of information about politics and public affairs seemed – Very high, Fairly high, Average, Fairly low, Very low.” John Zaller, among others, have argued that these ratings measure political knowledge reasonably well. However there is some evidence that challenges… Read more →

Correcting for Differential Measurement Error in Experiments

Differential measurement error across control and treatment groups or in a within-subjects experiment, pre and post-treatment measurement waves, can vitiate estimates of treatment effect. One reason for differential measurement error in surveys is differential motivation. For instance, if participants in the control group (pre-treatment survey) are less motivated to respond accurately than participants in the treatment group (post-treatment survey), the… Read more →

Against Proxy Variables

Lacking direct measures of the theoretical variable of interest, some rely on “proxy variables.” For instance, some have used years of education as a proxy for cognitive ability. However, using “proxy variables” can be problematic for the following reasons — (1) proxy variables may not track the theoretical variable of interest very well, (2) they may track other confounding variables,… Read more →