Recent content by AlexanderC

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    Question about the normality assumption

    This possibly was my bad wording -- i mean not important to check for when we run our test. In terms of what the underlying theory is about these statistical analysis, then I understand that it forms part of the proof and the entire thing rests on the assumption and that is fine. But my problem...
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    Question about the normality assumption

    It seems like there is general agreement about normality not being an important assumption then. But I am still unclear what to take away from this! For example if I run a t-test (or a whatever test), I need to make sure I meet its assumptions because when I send it off to Nature I will be...
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    Question about the normality assumption

    You said it is the sampling distribution of the thing we are looking at. But we do not have access to it as we don't run infinite experiments so we estimate it from our sample. So my confusion is why we should care about normality at all, because (1) if we can make a good argument that our...
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    Chi square on a huge dataset

    I have a situation where I want to look if a simulation gives expected values, so I think a chi squared is the way to do this. Some of the expected probabilities are quite tiny, but others are very large. After doing a chi square I noticed it gives a huge value = 867551.351! I see online that...
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    Question about the normality assumption

    I see everywhere reference to the normality assumption. e.g. for a t-test, you read "data must be approximately normally distributed". When reading more, you see for repeated measure t-test we want the difference to approximately be normal, and for independent we want values in each group to be...
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    Chance performance in a binary response task

    Hello, I am confused by something and wonder if someone can help. With a task of 100 trials that are either TRUE or FALSE, where 80 are TRUE, what is the chance performance if a subject can respond "Yes" or "No"? Is this determined by the number of response options, or by the ratio of...
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    False discovery and multiple test

    I see, so it is more something you say prior to running the testing? But then I'm having some problem understanding how we might interpret the situation when we do observe (e.g. 4) significant results. What would be the interpretation in that case?
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    False discovery and multiple test

    I'm reading about the familywise error rate here and trying to put it into perspective. According to this, we calculate FWER = 1 - (1 - alpha)^n. In their example n=10, and with alpha .05, they say this gives 40.1% chance of a type 1 error. Is this practically saying that if i run a study and...
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    Power and T1

    Ahh of course! A bigger standard error in denominator requires a larger difference in the numerator for a significant test result, meaning less chance of a Type 1. I see it now, thank you hlsmith (and fed2)
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    Power and T1

    People say that low power due to low sample size makes it more likely to miss a true effect (i.e. Type 2 error). But low sample size results in higher variability. This means e.g. with a t-test, one of our groups could be larger simply due to this variability, but nevertheless be significant. So...
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    Variability instead of means?

    Thank you for feedback. Well, I do see your point. I thought SD might (like variance) necessarily be not normal. I think we can say that any distribution of variances would not be normally distributed (as it is always positive, and we square to get there), so thought this might also be true for...
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    Variability instead of means?

    I think it is relevant because if I were to do a t-test (or ANOVA in a more complex scenario) to compare pre/post then this requires normality. Means might be fine, but when I was thinking on this, the variance cannot be normal, and I am not sure if the SD would be either.
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    Variability instead of means?

    Thank you for the idea. If I aggregate and end up with the SD can this be analyzed as if we are just analyzing the mean? e.g. t-test, ANOVA, so on. Or is this a violation of normality? I mean is the population standard DEV assumed to be a normal distribution? It feels a bit strange to think...
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    Variability instead of means?

    Hello, I was thinking about analysing variability instead of means but could not find much for an answer. I am interested in learning more about this so I would appreciate some feedback. I made some R code to demonstrate my question (I can't code well in R, improvements are much welcome too)...
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    Within-Subjects ANOVA with low sample

    Hello, I have some data that I want to analyse. It is 2x2 within-subjects design. My DV is continuous and the two factors have 2 categorical levels. But I only have 8 subjects, so I am unsure about how to proceed. Is it correct that there is no reasonable alternative to just using an ANOVA? If...