Hillary gaining momentum in Texas

One likely reason for much of the apparent "volatility" in the Democratic results is that the Obama-Clinton vote preference shows large variation on five critical variables: race and ethnicity, gender, age, socio-economic status and party affiliation (percent non-Democratic on party ID). Small changes in pollster methods (such as whether they sample from a list, how they select respondents within each sampled household, what time of day they call, whether they use live interviewers or an automated methodology and how they weight their data) can produce important differences in sample composition that will in turn affect the vote preference results.