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Archive for January, 2014

Null Hypothesis

After almost a year supervising students for conducting research and writing their final thesis, I found the students used to forget how to test hypothesis. First, students forgot to choose null hypothesis and the alternative before the sample is drawn. According to Kothari (2004), doing so can avoid the students from the error of deriving hypotheses from the data that he collects, and then testing the hypotheses from the same data. Please keep these considerations in mind when choosing the null hypothesis.

1. The null hypothesis is the one which the researcher wishes to disprove; alternative hypothesis is the one which the researcher wishes to prove. Hence, a null hypothesis represents the hypothesis we attempt to reject, and alternative hypothesis represents all other possibilities.
2. If the rejection of a certain hypothesis when it is actually true involves great risk, the researcher must take it as null hypothesis. It is because the probability of rejecting the hypothesis when it is true is α (the level of significance) which is chosen very small.
3. The null hypothesis should be simple and specific, not state about or approximately a certain value. For example, µ = µH0 is a null hypothesis; while µ = µH0 or µ = µH0 or µ = µH0 is a composite or nonspecific or alternative hypothesis.

Second, they forgot hypotheses that they supposedly measured were the null hypothesis. The one we test is the null hypothesis; this is the one that we try to reject. Mostly students derive hypothesis from assumptions, as they are convinced by theories and are suggested by findings of prior studies. The assumptions lead them to construct hypotheses that they wish to accept, not to reject. However, they forgot to reverse the statement and develop the null hypothesis. Instead, students tested hypotheses that they desire to accept, it is the one that consistent with theories and prior studies.

A study proceeds hypothesis testing on the basis of null hypothesis, while it keeps the alternative hypothesis in our mind. According to Kothari (2004), this is because on the assumption that null hypothesis is true, one can assign the probabilities to different possible sample results. But, this cannot be done if we proceed with the alternative hypothesis.

Reference: CR Kothari (2004), Research Methodology: Methods and Techniques, New Age International Publishers, India.

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