![]() ![]() So, we should select the sample from the population. If we want to collect data from all young people, we should spend a lot of time, money, energy. Collecting data from all young people in Vancouver is impractical. Suppose that we are interested in estimating average hight among young people in Vancouver. It is an important concept that should be considered when performing any type of data analysis. Higher degrees of freedom, less uncertainty, t-distribution will look more and more like a normal distribution.The Central Limit Theorem is the cornerstone of statistics. lower degrees of freedom, more uncertainty, fatter tails. So even if you standardize the variable, the distribution will depend on the degrees of freedom of the distribution. The t distribution "ratio" is larger than the one for normal distribution. In other words, once you standardized a variable, (so that it has a mean zero and standard deviation 1), if that variable follows a normal distribution, it will always look the same. However, a normal distribution has a very nice "ratio" of dispersion around the tails, and concentration around the means. In a normal distribution, the larger the variance, the farther the tails will spread. ![]() However, the larger the sample is, the more accurate the Standard deviation estimate will be, thus t-distribution will converge with the normal distribution. Since we do not know the standard errors, there is more uncertainty of the t-statistic. Why is t-distribution fatter? because there is more uncertainty. Your "title" question seems more clear to me than your detailed question. In my original idea of being on tail I would consider the area $ and $[\mu 3\sigma, \inf)$ and if some distribution has "fatter tail" would be to have large area under the curve in that tail area. So I wonder why Wikipedia has this definition of being "fat". In case of Exponentiation distribution 3rd and 4th moments are: 2 and 6, and in case of Normal distribution those moments are zero. It is pretty unclear why both the normal distribution or an exponential distribution are considered in here because their third and forth moment formula differs. So my hypothesis H looks like is wrong at the very start, because you cannot alter the Normal distribution "fat tail" state with the standard deviation parameter. ![]() In general, and I understood this for the first time thanks to " a fat-tailed distribution" is a probability distribution that exhibits a large skewness or kurtosis, relative to that of either a normal distribution or an exponential distribution according to Wikipedia It looks to me the answer is yes, for the previous question but maybe I am missing something important. Q: Is this comparison based on the normal distribution used to produce the t-distribution? H: In general you can control the tails of normal distribution with standard deviation, the bigger it is the fatter the tails so I can make the tails as fat as I like. I need to clarify the Hypothesis H and Question Q: and the population's standard deviation is unknown.when estimating the mean of a normally-distributed population. ![]()
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