What is statistical significance and how is the p-value calculated?

Statistical significance is a measure of how unlikely the obtained result of an experiment or test is, assuming the null hypothesis is true. If the result is statistically significant, it means that the probability of obtaining such a result by chance is very low, and the null hypothesis can be rejected.

p-value is the probability of observing data as extreme or more extreme than what was actually observed, assuming the null hypothesis is true. The smaller the p-value, the stronger the evidence against the null hypothesis.

To calculate the p-value, usually:

1. The null hypothesis is formulated (e.g., no difference between groups).
2. A test statistic is chosen (e.g., t-statistic).
3. The value of the statistic is calculated from the data.
4. The probability of obtaining such or more extreme values of the statistic from the distribution under the null hypothesis is determined — this is the p-value.

If the p-value is less than the pre-selected significance level (usually 0.05), the result is considered statistically significant.