Do swimmers go faster in the finals?

Case Studies in Statistical Thinking

Justin Bois

Lecturer, Caltech

Event	Time	Venue	Date	Round
100 m free	47.51	Beijing	2008-08-11	Final
200 m free	1:42.96	Beijing	2008-08-12	Final
400 m free	3:47.79	Indianapolis	2005-04-01	Final
100 m back	53.01	Indianapolis	2007-08-03	Final
200 m back	1:54.65	Indianapolis	2007-08-01	Final
100 m breast	1:02.57	Columbia	2008-02-17	Final
200 m breast	2:11.30	San Antonio	2015-08-10	Final
100 m fly	49.82	Rome	2009-08-01	Final
200 m fly	1:51.51	Rome	2009-29-07	Final
200 m IM	1:54.16	Shanghai	2011-07-28	Final
400 m IM	4:03.84	Beijing	2008-08-10	Final

Event	Time	Venue	Date	Round
50 m free	23.67	Budapest	2017-07-29	Semifinal
100 m free	51.71	Budapest	2017-07-23	Final
200 m free	1.54.08	Rio de Janeiro	2016-08-09	Final
400 m free	4.06.04	Amiens	2014-03-16	Final
50 m back	27.80	Borås	2017-06-30	Final
100 m back	59.98	Eindhoven	2015-04-05	Final
50 m fly	24.43	Borås	2014-07-05	Final
100 m fly	55.48	Rio de Janeiro	2016-08-07	Final

Your question

Do swimmers swim faster in the finals than in other rounds?

Do individual female swimmers swim faster in the finals compared to the semifinals?

Events: 50, 100, 200 meter freestyle, breaststroke, butterfly, backstroke

$$f = \frac{\text{semifinals time} - \text{finals time}}{\text{semifinals time}}$$

Original question:

Sharpened questions:

What is the fractional improvement of individual female swimmers from the semifinals to the finals?

Is the observed fractional improvement commensurate with there being no difference in performance in the semifinals and finals?

Case Studies in Statistical Thinking