OpinionWorks completed 798 telephone interviews Oct. 15-20 among likely general election voters across Maryland. According to customary statistical standards, this sample produces a margin of error of no more than 3.5 percentage points at a 95 percent confidence level. This means that 95 percent of the time, the "true" figure would fall within this range if every likely general election voter in Maryland had been interviewed.
Margin of sampling error is only one of many potential sources of error in this or any other public opinion survey. The practical difficulties of conducting any survey of public opinion introduce other sources of error into the study. Variations in the wording of questions or the order of the questions, for instance, can lead to somewhat different results.
The survey sample was drawn from an electronic database of Maryland registered voters supplied by the Maryland State Board of Elections and matched with telephone numbers by a commercial vendor.
Voter history codes on the file allow us to reach voters who have a track record of voting in past elections — in this case having voted in at least one of the last two gubernatorial general elections, or having registered to vote since the last general election.
Voters were screened to gauge their interest in voting in the Nov. 2 election. Those who gauged their likelihood of voting as 7 or higher on a 10-point scale were included in the survey sample.
Sampling quotas were adhered to throughout the interviewing process to reflect the distribution of voters across the state, based on partisan turnout patterns averaged over the past four general elections for seven major jurisdictions and regions of the state.
The final sample was weighted to bring it into compliance with the expected makeup of the electorate by political party and key demographics.
Results were weighted to reflect a higher-than-average expected Republican turnout this year, predicting that Republicans will make up 30 percent of the statewide electorate, and slightly lower African-American participation (19 percent) than in recent elections.
Steve Raabe is president of OpinionWorks, a nonpartisan independent polling and research company based in Annapolis that has conducted surveys for The Baltimore Sun for several years.