What is statistical significance?
The level of significance is generally taken as 5%. In some case, it can be 1% or 10% or 2%.
Here, let me explain the meaning of 5% level of significance.
By the property of a normal variate, we know that
#mu#- 3 #sigma#< x < #mu#+ 3 #sigma#] is approximately .95
In other words, it is expected that in only 5% cases, the value of the random variable is expected to be outside the range mentioned above.
Hence, a null hypothesis rejected by a statistical test procedure, we say that the difference is statistically significant.