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enter image description hereWhy is it necessary to have a DMSO alone control when DMSO has been used as the solvent (vehicle) in the treated conditions?

And, in this case, why is the viability of the untreated condition lower than the vehicle (DMSO alone)?

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closed as off-topic by canadianer, Bryan Krause, David, theforestecologist, another 'Homo sapien' May 31 '17 at 5:44

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  • $\begingroup$ It could simply be that the reagents or drugs involved dissolve well in DMSO and poorly in other solvents. Vehicles are a way of saying this is the drug/reagent + solvent. As always, when DMSO is the solvent, include DMSO-alone controls so you know the effect you're seeing isn't a result of the DMSO. $\endgroup$ – CKM May 30 '17 at 18:58
  • $\begingroup$ @CMyosychuk So we use it in order to know whether the drug or reagent itself that has effect on cell viability, right? And based on the above graph, why do the graph of Vehicle is higher than None? $\endgroup$ – Sokviseth May 31 '17 at 5:28
  • $\begingroup$ @Sokviseth Its not possible to give a clear 'why' answer to that question. The most probably reason is just biological variance, from your two different samples. Also note that the SD (which doesnt make a lot of sense for 2 samples anyway) for the vehicle control is very large. $\endgroup$ – Nicolai May 31 '17 at 5:33
  • $\begingroup$ As @Nicolai said, this is most likely simply variance, with more independent samples, the difference will probably be smaller. Additionally, given these error bars, I would see the untreated and the DMSO samples as the same. The treated samples are pretty much different from them. $\endgroup$ – Chris May 31 '17 at 6:29
  • $\begingroup$ @Sokviseth What's your measure here (the axis values)? If it's indeed a measure of viability, basically you're saying your drugs are dissolved in DMSO, and you want to see the effect of the drugs vs. no drugs. But, the DMSO can affect viability, too, so you have to do a DMSO alone condition. Your goal, however, is you actually want to say that the DMSO had no effect so you can see the pure effect of your drugs. The p-value between your none and vehicle is like 0.5, which means they aren't different, which is good because your drug readouts will have no/little background. $\endgroup$ – CKM May 31 '17 at 16:06