Types of hypothesis
A hypothesis (plural hypotheses) is a precise, testable statement of what the researchers predict will be the outcome of the study. This usually involves proposing a possible relationship between two variables: the independent variable (what the researcher changes) and the dependant variable (what the research measures). In research, there is a convention that the hypothesis is written in two forms, the null hypothesis, and the alternative hypothesis (called the experimental hypothesis when the method of investigation is an experiment). The hypotheses can be expressed in the following ways:
The two types of alternative hypothesis are: directional hypothesis and non-directional Hypothesis. A non-directional alternative hypothesis states that the null hypothesis is wrong. A non-directional alternative hypothesis does not predict whether the parameter of interest is larger or smaller than the reference value specified in the null hypothesis. Whereas a directional alternative hypothesis states that the null hypothesis is wrong, and also specifies whether the true value of the parameter is greater than or less than the reference value specified in null hypothesis. The advantage of using a directional hypothesis is increased power to detect the specific effect you are interested in. The disadvantage is that there is no power to detect an effect in the opposite direction.
Hence, therapists formulating a truly meaningful hypothesis must sometimes continue to look for causal links. They must continue to open themselves up to the experience of their clients in relation to themselves with the expectation that new and more specific material will shed new light. The client who relates a story about a verbally abusive bus driver encountered on the way to therapy, for example, may be unconsciously providing an explanation of an original experience of victimization. But she may also be saying that her therapist’s “taking” her along a certain therapeutic path feels abusive to her. By continuing to listen carefully, her therapist will receive confirmation of one, if not both, of her hypotheses. Alternately, she may know she must entertain others.
For our example, we formally state: The alternative hypothesis (H1) is that prenatal exposure to alcohol has an effect on the birth weight for the population of lab rats.