Home Cosmetic Science Talk Formulating General (P < 0.05) meaning in effectiveness of a product

• # (P < 0.05) meaning in effectiveness of a product

Posted by on March 26, 2021 at 3:49 am

What does (P < 0.05) mean when the effectiveness of a product is compared to another?

For example
In one study reductions in wrinkle depth were observed by expert assessment at both 4 and 8 weeks for the salicylic acid containing formulation compared to its placebo (P < 0.05).

3 Members · 4 Replies
• 4 Replies
• ### Pharma

Member
March 26, 2021 at 8:16 am
It means that the probability for the treatment being identical with placebo is quite small. Whether or not the statistical test used to obtain that p-value was the right one and whether or not the threshold of α=5% indicates a significant difference between the two groups remains questionable.
Furthermore, even a very small p-value can be regarded as insignificant, for example when the confidence interval of the treatment group is so large that it encloses the placebo group.
You have to read and understand a publication to be able to tell if there really is a difference. It’s all too easy to cheat with statistics.
• ### Abdullah

Member
March 26, 2021 at 9:25 am

@Pharma so a treatment with (P < 0.01) is better than (P < 0.05). Am i correct?

• ### OldPerry

Member
March 26, 2021 at 5:19 pm

@Abdullah - I don’t know if it is “better” but that does mean the difference is less likely due to chance alone.

Think of it this way.  p = 0.05 means if you conducted the same experiment 100 times, 5 of those experimental results are the work of chance alone. If p = 0.01 then only 1 time out of 100 would you expect the result to be due to chance alone.

p = 0.05  = 1 in 20
p = 0.01  = 1 in 100

For comparison, when they wanted to verify the existence of the Higgs Boson particle, they required to results to be accurate within p =3×10^-7.  That means 1 in 3.5 million.

• ### Abdullah

Member
March 27, 2021 at 1:04 am

@Perry thanks ????