IF you calculate
∆Ct = Ct[Housekeeping]-Ct[Target] ... and ∆∆Ct = (∆Exp.)-(∆Control)
THEN
∆∆Ct is a log-fold-change.
IF you calculate
∆Ct = Ct[Target]-Ct[Housekeeping] ... and ∆∆Ct = (∆Exp.)-(∆Control)
THEN
-∆∆Ct is a log-fold-change(logs to the base 2).
IF you calculate
∆Ct = Ct[Target]-Ct[Housekeeping] ... and ∆∆Ct = (∆Control)-(∆Exp.)
THEN
∆∆Ct is a log-fold-change(logs to the base 2).
If the fold change is, say, 0.2, it means that the expression level in the experimental condition is 0.2-fold the expression as in the control condition. This should be reported (and understood as) 80% down-regulation, because the expression level is decreased by 80% to 20% of the level under contr.cond.
For an up-regulation, the factor is larger than 1. If the result is for instance 3, it means that the expression under exp.cond. is 3 times as high as under contr.cond, you can also say that it changed by a factor of 2 or by 200% (2 times higher than under contr.cond.).
Souce: NovoPro 2018-02-26