"Margin of Error" is the sixth episode of the fourth season of the HBO original series The Wire. Written by Eric Overmyer from a story by Ed Burns & Eric Overmyer, and directed by Dan Attias, it originally aired on October 15, 2006.

The title refers to the results of a poll on voting intentions for the mayoral primary featured in the series. In statistical analysis, the margin of error expresses the amount of the random variation underlying a survey's results. This can be thought of as a measure of the variation one would see in reported percentages if the same poll were taken multiple times. The larger the margin of error, the less confidence one has that the poll's reported percentages are close to the "true" percentages, that is the percentages in the whole population.

This is made in reference of Norman chiding Carcetti for trying to handle the vote turnout of the primary election on his own. This also is in reference of Sergeant Hauk trying to lead an improper investigation on Marlo with the use of a camera obtained through improper protocol, as well as Namond becoming further immersed in the drug game.

Although credited, Frankie Faison, Deirdre Lovejoy, Clarke Peters, Wendell Pierce, and Andre Royo do not appear in this episode.

Churchgoers gather for services two days before the primary election. All three mayoral candidates (incumbent Mayor Clarence Royce, Councilman Anthony Gray and Councilman Tommy Carcetti) are in attendance at separate churches with their families. As Randy Wagstaff arrives at another church with his foster mother, Miss Anna, he is watched by Bodie Broadus and his crew of drug dealers including Little Kevin. Inside Reverend Franklin's church, other revelers enjoying the gospel music include Carcetti's deputy campaign manager Norman Wilson, State Delegate Odell Watkins, middle school teacher Grace Sampson and Carcetti staffer Gerry.

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