Definition of Hypothesis/Null Hypothesis

Hypothesis [singular]; -eses [plural]

  Hyop- (from Gk, fr) => under : beneath : down : deficient; or "less than normal"

-thesis [singular]; -ses [plural] (taken from fr. -tithenai = to put or lay down… more to do) or "the act of laying down"

What is the Hypothesis?

According to Webster and Dorland's Medical Dictionaries:

"A formulation of a natural principle based on inference from observed data."

• A tentative assumption made in order to draw out and test its logical or empirical consequences.

• An assumption or concession made for the sake of argument or an interpretation of a practical situation/condition taken as a ground for action.

Examples given in Dorland's Medical Dictionary:

1. Plank's Quantum Hypothesis states that energy is radiated or absorbed only in integral units equal to hn, where h = Plank's Constant, n = frequency of vibration.

2. Makeham's Hypothesis assumes that death is the consequence of two co-existing causes: a. chance, which is constant; and b. inability to withstand destruction, which progresses geometrically.

3. Woods-Fildes Hypothesis states that sulfonamides tend to replace paraaminobenzoic acid which is an essential metabolite for bacteria.

What is the Null Hypothesis?

• "Hypothesis of No Difference" or the Null Hypothesis states that there are no differences between two or more populations or observations.  For the Null Hypothesis to hold true:  For example, when samples are taken from the populations there will be no differences between mean values observed.
• "Requirements" for the Alternative Hypothesis to be "Accepted" or found true:   For example, the hypothesis (Null Hypothesis) must be "falsified."   Specifically, mean values of samples (observations) taken from two or more populations are different.