After applying a statistical test, an investigator gets the `p value' as 0.01. It means that:

The difference is not sigificant 1% times and significant 99% times [Ref Park, I8/e, p 650-6511 Repeat May 2005 While comapring two samples first we set up a hypothesis called Null hypothesis. Null hypothesis states that there is no significant difference betwee the two samples e.g. there is no difference between the effects of two diff. drugs. Whatever difference we see is due to chance only and is not significant. The P' value indicates the probability of the null hypothesis being true (i.e. probability of the difference b/w two samples occuring due to chance). i.e. the 'p' value of .01 (i.e. 1%) means that there is 1% chance of null hypothesis being true and 99% chance of it being false. hence it means that the probability of difference between two samples (or effect of two drugs) being insignificant is only 1%. and there is 99% chance of the difference being significant. By convention a Null hypothesis is rejected when p .05 (meaning that the difference is unlikely to have occured by chance).