Erratum to “Letter to the Editor” [Contraception 74 (2006) 349–350]

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The October 2006 issue of Contraception includes a letter from me [1] that reported corrections to a previously published paper [2]. We regret to inform you that we have recently discovered additional minor errors in this paper. Revised Table 3, Table 4 and a revised figure (Fig. 1) are attached. Several of the p values reported in the original text of the paper are also very slightly overestimated or underestimated. None of the errors affect the statistical significance of any findings or the interpretation of the results.

Table 3. Number and duration of menstrual cycles

	Cycle 1					Cycle 2
	Cycle week of entry into analysis
	All	1	2	3	4+
ECP study
Total number of cycles	113	3	32	52	26	111
Number of complete cycles	111	3	31	51	26	94
Complete cycles
Cycle length (days)
Median		10	19	26	31	27.5
Median adjusted for usual cycle lengtha		12.4⁎	18.3⁎	24.8⁎	29.3	25.5
Difference from usual cycle length (days)
Median		−18	−11	−3	1.5	−2
Median adjusted for usual cycle lengtha		−12.4⁎	−8.6⁎	−2.7⁎	2.1⁎	−0.7
Comparison study
Total number of cycles	843	89	297	214	243	798
Number of complete cycles	798	78	279	203	238	599
Complete cycles
Cycle length (days)
Median		27	28	28	31	28
Median adjusted for usual cycle length		25.7	27.4	27.6	31.4	26.7
Difference from usual cycle length (days)
Median		−1	0	0	2	0
Median adjusted for usual cycle length		−0.1	0.6	0.8	5.0	0.3

Table 4. Number and duration of menstrual periods

	Period 1					Period 2
	Cycle week of entry into analysis
	All	1	2	3	4+
ECP study
Total number of periods	111	3	31	51	26	94
Number of complete periods	108	3	30	49	26	91
Complete periods
Period length (days)
Median		3	5	6	7	6
Median adjusted for usual cycle lengtha		3.3⁎	5.3	5.8⁎	6.4⁎	5.6⁎
Difference from usual period length (days)
Median		0	1	1	1	1
Median adjusted for usual cycle lengtha		−1.3	0	0.2	1.0	0.3
Comparison study
Total number of periods	798	78	279	203	238	599
Number of complete periods	785	77	271	201	236	580
Complete periods
Period length (days)
Median		5	5	5	5	5
Median adjusted for usual cycle lengtha		4.8	5.1	5.1	5.0	5.0

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• Fig. 1. 

  Cycle length by cycle week of enrollment in ECP and comparison studies. Note: In this box and whisker plot, the line in the middle of each box is the median, the upper and lower edges of each box are the 25th and 75th percentiles, respectively, and the upper and lower ends of the whiskers are the 5th and 95th percentiles, respectively.

The entire analysis has now been redone by an independent statistician, and we are confident that we have identified, fixed and reported all errors. We apologize to you and your readers and appreciate your patience in this matter.

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References 

1. Raymond E. Minor error in our paper which was recently published in Contraception. Contraception. 2006;74:349–350
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2. Raymond EG, Goldberg A, Trussell J, Hays M, Roach E, Taylor D. Bleeding patterns after use of levonorgestrel emergency contraceptive pills. Contraception. 2006;73:376–381
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