# This hypothesis is called the null hypothesis denoted

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This hypothesis is called the null hypothesis , denoted by 0 H . The null hypothesis ( 0 H ) is a statement about the value of a population parameter which is assumed to be true unless sample results imply that it is not. Contrasting to the null hypothesis is the alternative hypothesis , denoted by 1 H . For example, we could set up the following alternative hypothesis: The mean weight of JC2 male students is more than 70 kg. Usually, we are hoping to reject null hypothesis and the alternative hypothesis is what we want to establish. In order to test the validity of 0 H , we consider observations made from a random sample taken from the population and perform a statistical test . We write the above statements concisely as 0 H : = 70 vs 1 H : > 70 8.1.2 1-Tail and 2-Tail Tests There are two types of test that can be performed, depending on the alternative hypothesis being made. These are 1-tail or 2-tail tests. (i) A 1-tail test is performed when the alternative hypothesis considers an increase or a decrease in the population parameter; (ii) A 2-tail test is performed when the alternative hypothesis considers any change in the parameter (either an increase or a decrease). For testing of population mean, we formulate the null and alternative hypothesis as follows: Null Hypothesis: 0 H : 0 (note: 0 is the assumed population mean) Alternative Hypothesis: 1 H : 0 (any change) 2-tail test 1 H : 0 (definite increase) 1 H : 0 (definite decrease) Example 8.1 : For each of the following situations in (a) to (c), write down the null and alternative hypothesis, and. state whether they are one or two-tailed tests. a) A machine packs flour into bags, with average mass, which are supposed to be 1000 g. After adjustments to the machine, the bags have mass that are more than 1000 g. 1-tail test

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