Null Hypothesis (1 of 4)
The null hypothesis is an hypothesis about a population
The purpose of
is to test the
viability of the null hypothesis in the light of experimental data.
Depending on the data, the null hypothesis either will or will not be
rejected as a viable possibility.
Consider a researcher interested in whether the time to respond to
a tone is affected by the consumption of alcohol. The null hypothesis
is that µ1
= 0 where
is the mean time to respond after consuming
alcohol and µ2
is the mean time to respond
otherwise. Thus, the null hypothesis concerns the parameter
and the null hypothesis is
that the parameter equals zero.
The null hypothesis is often the reverse of what the experimenter
actually believes; it is put forward to allow the data to contradict
it. In the experiment on the effect of alcohol, the experimenter
probably expects alcohol to have a harmful effect. If the
experimental data show a sufficiently large effect of alcohol, then
the null hypothesis that alcohol has no effect can be rejected.