Sunday, 1 May 2022

Falsifiability Theory and Null Hypothesis

Falsificationism

Falsificationism was propounded by Karl Popper, a philosopher of Science. This theory evolved out of the debate over the Problem of Induction, that we have already seen in a separate blog (Inductiinism).

To understand Falsificationism we need to understand both the problem of induction as well as what we understand by hypothesis.

What is hypothesis?


               A hypothesis is an imaginative hunch by the scientist to explain some phenomenon, to show the relationship between certain conditions or some cause effect relationships.             According to Ayala (1994) hypothesis  must have four criteria viz.

a. It should have logical consistency in that it has no logical contradictions.

Suppose one hypothesise that since All A is X  since All A is P and All P is X. It is logically consistent since they follow the rules of logic.

b. It should have some explanatory power in that it tells something that make the phenomenon under consideration more comprehensible.

c. It should be consistent with the theories or knowledge related to the phenomenon under consideration that are already established, at least most of the times.

d. It should be testable i.e. the logical deductions or consequences derived logically from the hypothesis can be tested and are tested to establish the tenability of the hypothesis as an explanation. This condition thus represent the critical aspect of the hypothesis.

Falsification Theory

During the twentieth century, Karl Popper contributed towards the consolidation of the HDM through his falsification theory, that stands close to the idea that scientific method is basically deductive in nature.
        According to Falsification theory, the test of a scientific hypothesis is not its verifiability or its confirmation. Rather the test is the falsifiability of the hypothesis or its refutation. 

        The hypothesis formulated by the scientists as an explanation for a phenomenon, need to be "capable of being falsified through empirical observations" (ibid, p.228). Falsification is a better test for knowledge claims since Verification is always inconclusive, as was highlighted through the Problem of Induction by Hume. Verification process can yield innumerable instances of positive results, and yet it is always possible to have a negative observation that can challenge the validity of the conclusion. Innumerable instances of observation of swans and invariable observation of their white color can lead to the theory that “All Swans are white in color”. However, a single observation of black swan can make the theory skeptical or refute the theory. 
       As against such naive Inductivism, Popper favoured the hypothetical model of scientific method. The scientist creates hypothesis and through repeated efforts to falsify the hypothesis, the scientist is led towards new knowledge. 

        This falsification theory follows the procedure of using double negatives. First the scientists conjecture is expressed in a negative way. Logical deductions are derived from this hypothesis that are then tested to falsify them. If they are falsified, by observations that are contrary to the prediction, the scientists hypothesis is accepted as valid explanation.
     Thus science moves ahead through the process of falsification of hypothesis rather than through confirmation of the hypothesis. New knowledge emerges through falsification of the null hypothesis. Poppers favoured taste for falsification rather than confirmation was based on logical arguments.


Consider the syllogism:
 Modus Ponens.                                       Modus Tolens


If H then P.                                                     If H then P
P.                                                                     Not P
Therefore H                                             Therefore not H

  Popper argues that even through several instances of confirmation of P one cannot prove H to be true. There may be other reason why P is observed beside H. However, if we see the syllogism in B, a refutation of P necessarily shows that H cannot be true. Thus modus tollens is the syllogism that guides scientific method. Instead of imposing their own hypothesis, the scientists assume the no relationship hypothesis as true. They then make predictions from the null hypothesis. When predictions are not observed as expected, following modus tollens, the no relation hypothesis is refuted. Refutation of the null hypothesis leads to acceptance of the researcher hypothesis. If one fails to falsify the no relation hypothesis, it logically leads to unacceptability of the original hypothesis.
.               

ChiSquare Test

Chi Square https://docs.google.com/presentation/d/12d-tesJLFvRWe0S6McerPgghPcd_ctF16StvS-BFB8Q/edit?usp=drivesdk