What is the usefulness of P-value in the Statistics.

All things being equal, and probably an item that has never been tested before, the test level is already predicted before any information is collected. I guess the only usefullness is the P value is used to fill in the gaps.

"P-Value of a statistical test is a probability number that measures the extent to which the sample data are consistent with the Null hypothesis. It represents a compact summary of sample findings in a statistical test....."

(See page 329, Applied Statistics, By John Neter, 3rd Edition)

FURTHER: See P-value - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/P-value)

"In statistical hypothesis testing, the p-value is the probability of obtaining a result at least as extreme as a given data point, under the null hypothesis. The fact that p-values are based on this assumption is crucial to their correct interpretation"