There are two hypotheses in statistical tests, called the null hypothesis, often written as formula_1, and the alternative hypothesis, often written as formula_2. The null hypothesis states that there is no link between the phenomena, and is usually assumed to be true until it can be proven wrong beyond a reasonable doubt. The alternative hypothesis states that there "is" some kind of link. It is usually the opposite of the null hypothesis, and is what one would conclude if null hypothesis is rejected. The alternative hypothesis may take several forms. It can be two-sided (for example: there is "some" effect, in a yet unknown direction) or one-sided (the direction of the supposed relation, positive or negative, is fixed in advance).