A statistical estimate of the population parameter.

I think you are asking: What is hypothesis testing in the field of statistics. See: http://en.wikipedia.org/wiki/Statistical_hypothesis_testing

A hypothesis is the first step in running a statistical test (t-test, chi-square test, etc.)

A NULL HYPOTHESIS is the probability that what you are testing does NOT occur.

An ALTERNATIVE HYPOTHESIS is the probability that what you are testing DOES occur.

A non-directional research hypothesis is a kind of hypothesis that is used in testing statistical significance. It states that there is no difference between variables.

Herman J. Loether has written:

'Inferential statistics for sociologists' -- subject(s): Sampling (Statistics), Sociology, Statistical hypothesis testing, Statistical methods

'Descriptive and inferential statistics' -- subject(s): Sampling (Statistics), Sociology, Statistical hypothesis testing, Statistical methods

'Descriptive statistics for sociologists' -- subject(s): Sociology, Statistical methods