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week2 - ECONOMETRICS(ECON346 1 Distribution The...

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ECONOMETRICS (ECON346) 1. Distribution The distribution of a data set is a table, graph, or formula that provides the values of the observation and how often they occur (probability). 1.1 Distribution Shapes The shape of a distribution can be described in terms of symmetry & kurtosis With a symmetrical distribution a vertical line can be drawn through the middle so that each side is a mirror image of the other. With a skewed distribution the scores tend to pile up at one end and tail off at the other. If the tail is to the right the distribution is said to be positively skewed, if the tail is to the left it is negatively skewed. Symmetric Bell-shaped Right Skewed (Positive Skewed) Left Skewed (Negative Skewed) Bimodal
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ECONOMETRICS (ECON346)
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ECONOMETRICS (ECON346)
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ECONOMETRICS (ECON346) 2. SAMPLING Population : The entire group of items that interests us. Defined by the characteristics Sample : The part of population that actually observed. Why sampling To draw inferences about the population since it is often impractical to scrutinize the entire population. It is too expensive to apply to the entire population. Biased Sample : Any sample that differs systematically from the population. It can give the distorted picture of the population and may lead to unwarranted conclusion. 1) Sample Selection Bias : The selection of samples systematically excludes or under-represents certain group. Self-selection bias 2) Survivor Bias : a sample from a current population in order to draw inferences about a past population who are no longer around.
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