По-английски статистическая значимость - обычно одно слово significant, статистически достоверные отличия - significantly different. Statistically пишут реже. Например:

A significant reduction in patient's sleep loss - Статистически достоверное сокращение потерь сна

X was significantly different compared to placebo - Статистически достоверные отличия между X и плацебо

both X and control treatment groups experienced a significant improvement in the quality of life - в обеих группах, Х и контроля, зафиксировано статистически значимое улучшение качества жизни


Cholesterol levels were slightly elevated in the breast cancer group and mean values were significantly different compared to our control group.
linkinghub.elsevier.com/retrieve/pii/0014296475900511

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Note added at 21 mins (2010-08-09 20:48:10 GMT)
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Или from (еще чаще, чем compared to):

During Days 19 to 24 (oestrous period), there were no
significant differences between Groups 1, 2 and 3 but all these groups
were significantly different from Group 4 (P< 0-001).
http://www.reproduction-online.org/cgi/reprint/21/1/127.pdf

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Note added at 1 hr (2010-08-09 22:19:44 GMT)
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To Wendy:

I know very well what statistical significance is. In practice, however, the word "statistical" is more often left out than not. Just "significantly different" is a very common and accepted way to refer to a statistically significant difference, and is perfectly well understood.

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Note added at 2 hrs (2010-08-09 22:54:58 GMT)
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Еще примеры из 204 000 по запросу "significantly different"+"treatment groups" (я специально взяла такие ключевые слова, чтобы отобрать контексты, где сравниваются группы терапии). Обратите внимание, что везде указана величина p (вероятность того, что гипотеза о статистической достоверности различий неверна), т. е. "significantly different" означает именно статистически достоверные отличия.

The study group increased from 43.1 to 45.2 to 71.0 to 81.9 and were significantly different (p = NS, < 0.05, < 0.001, 0.06).
http://www.shoulderdoc.co.uk/article.asp?article=1347

Body temperatures of the two species (Fig. 6) were similar at
Epanomi (t-test, P > 0.5) but were significantly different at
Lagos (P < 0.05) and especially at Keramoti (P < 0.001).
http://www.ahailey.f9.co.uk/pdf/wsh1988.pdf

The sum of changes from baseline in swollen throat over 15 to 120 minutes was significantly different between treatment groups (p = 0.028).
www.medscape.com/viewarticle/406217_3

The treatment changes in this region were significantly different from the control group (P < .001).
www.angle.org › The Angle Orthodontist › December 2004

*Pre- and post-treatment MDA levels were significantly different in group 2 (P< 0.005).
www.springerlink.com/index/42166L8441471778.pdf

Note that the group treated with Survanta 50 mg/kg with PEG is significantly different from both injured control animals and animals treated with either 50 or 100 mg/kg of Survanta alone (two-way ANOVA with repeated measures, p < 0.05).
http://ajrccm.atsjournals.org/cgi/content/full/162/2/623

Superscript letters denote mice with values significantly different (P < 0.05) from mice of the same strain in different treatment groups
http://www.biomedcentral.com/1471-2172/11/39/table/T1