Κι εγώ στην αρχή νόμιζα πως αναφέρεται στα μονοζυγωτικά δίδυμα, αυτά που ξέρουμε πως μοιάζουν σαν δυο σταγόνες νερό, αλλά έκανα λάθος και το ξαναέψαξα λίγο παραπάνω, κι έτσι αναφέρεται στα conjoined twins or cotwins, και τα παρακάτω μέσα στο άρθρο.
https://en.wikipedia.org/wiki/Conjoined_twins
https://en.wikipedia.org/w/index.php?search=co-twins&title=S...


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Note added at 21 ώρες (2022-05-07 09:49:47 GMT)
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https://www.wordreference.com/enfr/conjoint
CONJOINT OR SIAMOIS, en français, in french

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Note added at 21 ώρες (2022-05-07 09:55:17 GMT)
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https://onlinelibrary.wiley.com/doi/10.1002/0470013192.bsa14...
Co-twin Control Methods
The co-twin control method is an elegant research design that uses differences within twin pairs to examine the association between a putative environmental risk factor and an outcome variable. The design is extremely efficient for examining risk factor–outcome associations compared to unmatched designs. This is especially true when using monozygotic (MZ) twins who share 100% of their genetic material. Co-twin control studies can be used in both the experimental and observational settings. Statistical analysis for continuously distributed outcome variables focuses on the within-pair mean difference, while for dichotomous outcomes, the matched pair odds ratio is used. Whenever possible, it is informative to examine differences in the relationship between the risk factor–outcome association by zygosity; findings that are only present in dizygotic (DZ) pairs suggest that the observed association may be due to genetic influence on both the risk factor and outcome. We present an illustration of the analysis of a co-twin control study, looking at the association between military service in Vietnam and posttraumatic stress disorder, with data from the Vietnam Era Twin Registry. A wide range of new regression modeling methods, which account for nonindependent observations, can be readily adapted for co-twin control studies.

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Note added at 21 ώρες (2022-05-07 09:57:18 GMT)
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https://pubmed.ncbi.nlm.nih.gov/33197098/
https://www.twins.org.au/research/twin-study-designs/94-co-t...
https://www.sdu.dk/-/media/files/om_sdu/institutter/ist/epid...
https://www.keananjoyner.com/full_publications/Joyner et al....
https://www.midus.wisc.edu/findings/pdfs/1520.pdf

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Note added at 22 ώρες (2022-05-07 10:44:29 GMT)
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The co-twin control method is an elegant research design that uses differences within twin pairs to examine the association between a putative environmental risk factor and an outcome variable. The design is extremely efficient for examining risk factor–outcome associations compared to unmatched designs.
ΕΝΤΕΛΕΙ, βγάζω το συμπέρασμα ότι έτσι ονομάζεται η εν λόγω μέθοδος ανάλυσης των διδύμων, co-twin method analysis, έχει σχέση με τα δίδυμα, μονοζυγωτικά και διζυγωτικά.

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Note added at 22 ώρες (2022-05-07 10:58:55 GMT)
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Definition of co-twin
: the birth partner of a twin.
https://www.merriam-webster.com/dictionary/co-twin

Co-twin Control Studies
If both of the twins have some health problem, we offer the treatment to only one of them and then we compared the results of the cure. It is not ethical to try with the drug therapy.

E.g. there was a research few years ago, when the doctor tried to teach one of the twin to climb the stairs, the second twin didn´t practice it. However, both of them were able to climb the stairs after few weeks, the trained one did it a week earlier. It shows that the environmental influence could help them to learn something faster, but at the end the results were the same for both of the children.
https://www.wikilectures.eu/w/Twins_and_Twin_Studies#Co-twin...