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quote:The normal distribution, also called Gaussian distribution, is an extremely important probability distribution in many fields. It is a family of distributions of the same general form, differing in their location and scale parameters: the mean ("average") and standard deviation ("variability"), respectively. The standard normal distribution is the normal distribution with a mean of zero and a standard deviation of one (the green curves in the plots to the right). It is often called the bell curve because the graph of its probability density resembles a bell. The fundamental importance of the normal distribution as model of quantitative phenomena in the natural and behavioral sciences is due to the central limit theorem (the proof of which requires rather advanced undergraduate mathematics). A variety of psychological test scores and physical phenomena like photon counts can be well approximated by a normal distribution. While the mechanisms underlying these phenomena are often unknown, the use of the normal model can be theoretically justified if one assumes many small (independent) effects contribute to each observation in an additive fashion. The normal distribution also arises in many areas of statistics: for example, the sampling distribution of the mean is approximately normal, even if the distribution of the population the sample is taken from is not normal. In addition, the normal distribution maximizes information entropy among all distributions with known mean and variance, which makes it the natural choice of underlying distribution for data summarized in terms of sample mean and variance. The normal distribution is the most widely used family of distributions in statistics and many statistical tests are based on the assumption of normality. In probability theory, normal distributions arise as the limiting distributions of several continuous and discrete families of distributions.
Measurement Observed Cumulative Estimated Estimated frequency observed frequency cumulative frequency frequency 0 2 2 1.3 1.3 1 3 5 2.4 3.7 2 4 9 3.8 7.5 3 3 12 4.9 12.4 4 4 16 5.4 17.8 5 7 23 4.9 22.7 6 3 26 3.8 26.5 7 3 29 2.4 28.4 8 2 31 1.3 30.2 9 1 32 0.6 30.8
quote:Originally posted by 4getmenotI do not see how this stuff comes easy to others...man...this is truely ging to give me grey hair...