Level of significance and acceptance and rejection of the null hypothesis

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Discussion Overview

The discussion revolves around the concepts of hypothesis testing, specifically the rejection and acceptance of the null hypothesis in the context of the Chi-square goodness of fit test. Participants explore the implications of Chi-square values in relation to significance levels and the interpretation of p-values.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that the null hypothesis is not "accepted" but rather "failed to be rejected," emphasizing the distinction in terminology.
  • There is a discussion on the implications of having a Chi-square statistic that is less than or greater than the tabulated value at a given significance level, with some suggesting that a smaller statistic indicates a good fit and thus should not lead to rejection of the null hypothesis.
  • Others propose that if the Chi-square value is less than expected, it suggests a higher possibility of rejecting the null hypothesis, while a larger value indicates a lower possibility of rejection.
  • One participant raises the question of whether the discussion pertains to the Chi-square statistic itself or the broader procedure of hypothesis testing, noting that hypothesis testing lacks definitive mathematical theorems that guarantee correct decisions.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of Chi-square values and the acceptance or rejection of the null hypothesis. There is no consensus on the implications of these values, and the discussion remains unresolved regarding the clarity of the hypothesis testing procedure.

Contextual Notes

Participants highlight the arbitrary nature of the 5% significance level and the potential for shifting this threshold based on specific requirements. There is also mention of the need for clarity on whether the discussion is focused on the Chi-square statistic or the general hypothesis testing framework.

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Why do we reject the null hypothesis in Goodness of fit when the Chi square statistic is less than the tabulated value of chi-square at say 5% level of significance and accept when it is more?

What does it mean to have a Chi-square value more or less than the value assigned to a certain level of significance?

Edited: The homogeneity thing was wrong, so I removed it.
 
Last edited:
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1. We don't "accept" the null hypothesis we simply fail to reject it.
2. Basically, you're simply saying given some assumptions regarding the data, if the null hypothesis were true and I had a p-value of .00001, then it would be highly unlikely (but not impossible) for that data to come from the same distribution. The 5% is rather arbitrary and depending your requirements may be shifted to the left or right.
 
MarneMath said:
1. We don't "accept" the null hypothesis we simply fail to reject it.

Thank you.
How do we comment or conclude at the end of a goodness of fit, when the observed X2 i.e. less than the expected X2, the X2 corresponding to a particular significance level?
2. Basically, you're simply saying given some assumptions regarding the data, if the null hypothesis were true and I had a p-value of .00001, then it would be highly unlikely (but not impossible) for that data to come from the same distribution. The 5% is rather arbitrary and depending your requirements may be shifted to the left or right.
I just realized what I wasn't getting for so long-
If suppose the level of significance is constant (can't be changed) then a less than expected X2 means increased possiblility that a true null hypothesis can be rejected and is indeed rejected and if larger than expected X2, it means lesser possibility of not being rejected and we say we fail to reject?
 
SanjuktaGhosh said:
Why do we reject the null hypothesis in Goodness of fit when the Chi square statistic is less than the tabulated value of chi-square at say 5% level of significance and accept when it is more?

What does it mean to have a Chi-square value more or less than the value assigned to a certain level of significance?

Edited: The homogeneity thing was wrong, so I removed it.
Do you mean the statistic or the P-value?
The null hypothesis is typically that the data comes from a hypothesized distribution.
The statistic of the Chi-square is small when there is a good fit between the data and the hypothesized distribution. So you should not reject the null hypothesis if the statistic is small.

On the other hand, the P-value is large when there is a good fit between the data and the hypothesized distribution. So you should reject the null hypothesis if the P-value is small.
 
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SanjuktaGhosh said:
What does it mean to have a Chi-square value more or less than the value assigned to a certain level of significance?

It's difficult to tell whether your questions are about the chi-square statistic in particular or whether you need to know about the general procedure of hypothesis testing. As to the general procedure of hypothesis testing, it is important to know that it is not a form of mathematical deduction. There are no mathematical theorems that say you must do this-or-that when you apply hypothesis testing and there are no mathematical theorems that say you will make a correct decision by using hypothesis testing. Hypothesis testing is simply a procedure that has some intuitive appeal and is thought to be empirically effective in certain fields of study.
 

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