By: bozemanbiology | Minutes: 11:53 | Views: 137,570 Uploaded: November 13th, 2011 (1 year, 7 months ago)

Paul Andersen shows you how to calculate the ch-squared value to test your null  hypothesis.  He explains the importance  of the critical value and defines the  degrees of freedom.  He also leaves you  with a problem related to the animal  behavior lab.  This analysis is required in the AP Biology classroom.

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Show/Hide 25 Comments

Gabriel Mendoza: thanks heaps, got a statistics test coming up, helped a lot! only thing is my lecturer say never to say 'accept the null hypothesis' rather to say do not reject the null hypothesis Also there is nothing about p-values, I wasnt really looking for it but just thought i'd mention it thanks :)

theistheis: I thought that "accepting" a hypothesis, would imply that it was without a doubt TRUE, therefor not a suitable word.. I've been taught to use "failed to reject", thereby not implying that its without a doubt true, but instead that we accept the hypothesis in lack of data telling us otherwise.

TwyTwyVV: Is the null hypothesis the same for every test? my sum of value (weird looking E) was 0.04336, and I have taken this for five different temperatures, so if it was level of probability would be 0.05 = 9.49, this means I have to accept my null hypothesis? Is this correct? Thanks heaps :)

Tanzim Arefin: @bozemanbiology why are you using only 0.05 column to find your critical value? what does this represent?

kaboom cha: Fantastic! helps massively....but will i remember this during the exam? that is the question..

soccerlover70: Degrees of freedom is 1 not 9. There are only 2 outcomes. Just like the dice experiment, there were 36 experiments, but there are only 6 outcomes.

Taha Toriq: Very helpful, thanks!

fbztnt: Really good video understood everything! Thanks

Rhys Williams: 1 we have two possibilities head or tails 2-1 = 1

Luong Thai: I think there are 1 degree of freedom here. Even he did the experiment 10 times. There are only 2 outcomes: wet and dry. Therefore, 2-1 = 1 degree of freedom. I use the average number to calculate the chi-sq value. Since there are 2 outcomes, the chi-sq is basically the sum of those 2 outcomes, wet and dry. I got 6.084 for the chi-sq and with p=0.05 at 1 degree of freedom, I reject the null hypothesis (because 6.084 > 3.841). Conclusion, the animal behavior to stay in wet or dry is not random.

James Harrell: Revised: Your chi square is 15.21. Your critical value is 10-1=9 (16.919) of the 0.05. Accept the no significant differences.

James Harrell: Your chi square is 15.21. Your critical value is 10-1=9 (16.919) or the 0.05. Accept the significant differences.

Jackie Hao: You cant accept the null hypothesis, you can only fail to reject it!

Todd Aillon: Can someone explain whether it is 10 degrees of freedom or 1 degree of freedom? People in the comments are posting answers with both. (personally i think its 10)

ariesfairies: I've failed my Statistics class once, second time going now, 2 Lecturers have attempted teaching me Chi Squares.. well not blaming their methods, but finally I understood this! Thank you good sir!!

Perla Gutierrez: Thank you! A sample of less than 30 behaves different like a curve named T-Student or other curves. So to be in the Normal Curve it is better if you have at least 30 or more values. :D I like your. video! :D

Simi kaur: Oh yea...cramming is always good

OKlivy: Only a week after the AP exam my teacher gives us the final for the class. As if I didn't already have enough going on in my life in the last month of school. At least I have your videos to help me! Seriously though, these videos have been such great helps to me all year. AP biology was one of the hardest classes i've ever taken and I wouldn't have been able to get a decent grade without the great explanations you give in your videos. Thank you so much!

sportsbar wikileaks: very well explained! thanks

João Paredes: No último problema, como foi feita uma média, não se devia considerar 0 graus de liberdade? Eu fiz o problema considerando apenas 1 grau de liberdade. Dessa forma posso afirmar com 95% de certeza que o comportamento animal foi diferente do previsto. Chi-2 real= 6,084; Chi-2experimental= 3,841. 6,084>3,841

Vanessa Lovenburg: I get a chi-squared value of 6.084, and with a df of 10 (11 observations-1) which has a critical value of 3.94 (for p=0.05) you would reject the null hypothesis (there is no difference between observed and expected) since it's a higher value. Meaning that there is a statistically significant difference in the observed and expected times, and we are 95% confident that this difference is not by chance. Happy bugs are wet bugs!

amy ibrahim: so is it true that when we reject the value (higher than chi square),,does this mean(null hypothesis) that there is a huge difference between the observed and expected value..?

Emma Peacock: LOVE YOU!!!!!! 

tuberesu: I hope you all passed! . I hated stat sig when I was at university and this video is one of the best I have seen.

1337Note: At 10:51 if we would have had 0.1 as a critical value we would have hade to reject the null hypotosis. what does this mean ? 95 % chance that is's true 90 % chans that is false? tnx

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