Hypothesis

Primary hypothesis

The primary (or alternative) hypothesis (or just the first in a long list) is often written as H_1.

Experiments often seek to prove the primary hypothesis to be true and may be considered to have 'failed' if this is not achieved. In reality, an experiment succeeds when it correctly concludes that the primary hypothesis is true or false. It only fails when its conclusions are incorrect (or that a correct conclusion is incorrectly reached).

Null hypothesis

The null hypothesis (often written as H₀) is the opposite of the primary hypothesis in that it includes all other outcomes.

Note that if H₁ is that X happens, then H₀ includes both Y happens (which is other stuff) and that nothing happens. 'Not X' means anything but that which is predicted by the primary hypothesis.

For example if you hypothesize that feeding cats dog biscuits will make them purr more, then the null hypothesis would include both that feeding cats dog biscuits makes them purr less or feeding them dog biscuits does not change their purr rate.

Proving the null hypothesis false is an effective way of proving the primary hypothesis true and is an implementation of Karl Popper's falsification rule in his Hypothetico-deductive model.

Not guilty

Experiments that show that the null hypothesis is true do not necessarily show that the primary hypothesis is always false, only that it is not true in this situation. This is the same principle in law where a person is found not guilty (but not necessarily innocent).

Rather than giving up when their primary hypothesis is not proven, many researchers will simply return to their studies, seeking more specific conditions in which it may be proven true.

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Hypothesis

Definition

Primary hypothesis

Null hypothesis

Not guilty

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