Statistical Analysis of Predicted and Actual Results
for the Olympic Swimming Trials at Indianapolis in 2000
								95%	95%
						Standard		Confidence	Confidence
	Predicted	Actual			Standard	Error of	t	Interval	Interval
Event	Results	Results	Error	%Error	Deviation	the Mean	value	Lower	Upper
M50 Free	22.54	22.26	-0.28	-1.24	0.37	0.13	-2.14	:21.95	:22.57
M100 Free	49.79	49.44	-0.35	-0.70	0.78	0.28	-1.27	:48.79	:50.09
M200 Free	109.66	108.73	-0.93	-0.85	1.17	0.41	-2.25	1:47.75	1:49.71
M400 Free	233.73	232.33	-1.40	-0.60	4.09	1.45	-0.97	3:48.91	3:55.75
M1500 Free	924.23	918.90	-5.33	-0.58	12.37	4.37	-1.22	15:08.56	15:29.24
M100 Back	55.31	55.29	-0.02	-0.04	0.71	0.25	-0.08	:54.70	:55.88
M200 Back	120.33	120.13	-0.20	-0.17	1.83	0.65	-0.31	1:58.60	2:01.66
M100 Br	62.33	61.96	-0.37	-0.59	0.87	0.31	-1.20	1:01.23	1:02.69
M200 Br	135.54	135.57	0.03	0.02	2.58	0.91	0.03	2:13.41	2:17.73
M100 Fly	53.87	53.58	-0.29	-0.54	0.53	0.19	-1.55	:53.14	:54.02
M200 Fly	119.53	119.08	-0.45	-0.38	1.76	0.62	-0.72	1:57.61	2:00.55
M200 IM	122.29	123.36	1.07	0.87	1.80	0.64	1.68	2:01.85	2:04.87
M400 IM	261.17	260.94	-0.23	-0.09	6.51	2.30	-0.10	4:15.50	4:26.38
								95%	95%
						Standard		Confidence	Confidence
	Predicted	Actual			Standard	Error of	t	Interval	Interval
Event	Results	Results	Error	%Error	Deviation	the Mean	value	Lower	Upper
W50 Free	25.63	25.46	-0.17	-0.66	0.34	0.12	-1.41	:25.18	:25.74
W100 Free	55.64	55.28	-0.36	-0.65	0.64	0.23	-1.59	:54.74	:55.82
W200 Free	120.84	121.12	0.28	0.23	0.46	0.16	1.72	2:00.74	2:01.50
W400 Free	253.18	253.01	-0.17	-0.07	3.14	1.11	-0.15	4:10.38	4:15.64
W800 Free	520.93	516.38	-4.55	-0.87	8.04	2.84	-1.60	8:29.66	8:43.10
W100 Back	62.24	62.36	0.12	0.19	0.33	0.12	1.03	1:02.08	1:02.64
W200 Back	133.43	135.11	1.68	1.26	1.85	0.65	2.57	2:13.56	2:16.66
W100 Br	70.23	69.00	-1.23	-1.75	1.24	0.44	-2.81	1:07.96	1:10.04
W200 Br	149.50	149.00	-0.50	-0.33	2.73	0.97	-0.52	2:26.72	2:31.28
W100 Fly	60.17	59.49	-0.68	-1.13	1.19	0.42	-1.62	:58.49	1:00.49
W200 Fly	132.08	132.84	0.76	0.58	2.35	0.83	0.91	2:10.88	2:14.80
W200 IM	135.99	136.32	0.33	0.24	1.72	0.61	0.54	2:14.88	2:17.76
W400 IM	290.00	287.18	-2.82	-0.97	3.99	1.41	-2.00	4:43.84	4:50.52
The significant differences (shown in blue) were for Women's 200m Backstroke (significantly slower than predicted)
and for Women's 100m Breaststroke (significantly faster than predicted).

What is the 95% confidence interval?

The purpose of our study was to compare the actual times from the Olympic Trials with what was predicted based on previous trials. To make this comparison, we do not require the times to agree exactly since chance alone may account for part of the difference. Close is good enough. But how close do the times have to be for us to say that they are the same? The 95% confidence interval is a statistical method used to determine whether or not the difference between the predicted time and the actual time is due to chance alone or a real effect of something new and unexpected, like the body suit. So, if the 95% confidence interval contains the predicted time, then we are 95% confident that the actual time and predicted time are not different. Of course, there's a 5% chance that we are wrong. In statistics, being wrong only 5% of the time is considered to be good enough!