Florida Mass Shooting, Orlando, June 12

Orlando, Florida (CNN)An American-born man who'd pledged allegiance to ISIS gunned down 49 people early Sunday at a gay nightclub in Orlando, the deadliest mass shooting in the United States and the nation's worst terror attack since 9/11, authorities said.

The gunman, Omar Mateen, 29, of Fort Pierce, Florida, was interviewed by the FBI in 2013 and 2014 but was not found to be a threat, the FBI said.

Mateen called 911 during the attack to pledge allegiance to ISIS and mentioned the Boston Marathon bombers, according to a U.S. official.

Orlando police shot and killed Mateen. Mateen's ex-wife said she thinks he was mentally ill. Mateen carried an assault rifle and a pistol into the packed Pulse club about 2 a.m. Sunday and started shooting, killing 49 people and wounding at least 53, officials said.

Specific Hypothesis and Results

The GCP event was set for the 24 hour UTC day, and includes several hours before the attack, and substantial time after. The result is Chisquare 86269.931 on 86400 df, for p = 0.622 and Z = -0.311. The likely time the attack began is marked on the figure.

Interpretation

The following graph is a visual display of the statistical result. It shows the second-by-second accumulation of small deviations of the data from what’s expected. Our prediction is that deviations will tend to be positive, and if this is so, the jagged line will tend to go upward. If the endpoint is positive, this is evidence for the general hypothesis and adds to the bottom line. If the endpoint is outside the smooth curve showing 0.05 probability, the deviation is nominally significant. If the trend of the cumulative deviation is downward, this is evidence against the hypothesis, and is subtracted from the bottom line. For more detail on how to interpret the results, see The Science and related pages, as well as the standard caveat below.

Standard caveat

It is important to keep in mind that we have only a tiny statistical effect, so that it is always hard to distinguish signal from noise. This means that every success might be largely driven by chance, and every null might include a real signal overwhelmed by noise. In the long run, a real effect can be identified only by patiently accumulating replications of similar analyses.