Hypotheses

When using inferential tests such as Tests for Difference, hypotheses must be considered and constructed appropriately. 

A hypothesis is an assumption about how two or more variables are related. A simple hypothesis makes a prediction on how the independent variable/s will affect the dependent variable. Hypothesis statements are created prior to conducting any research and drive the future study, because one of the main aspects of inferential tests is to generalise the findings to the wider population. It makes sense to try and predict what these findings might be. Let’s say, for example, you are interested in crime; you want to explore whether age affects likelihood to be a victim of crime. We can develop a hypothesis from this, for example: 

Younger people are more likely to be a victim of crime than older people. 

But we must remember, our aim isn’t to just be referring to our sample, we want to know if this statement is true for the wider population.

Inferential statistical tests call for us to develop two statements, known as the Null Hypothesis and the Research Hypothesis. These statements should mirror one another, being they follow the same structure. One (the Null Hypothesis) is the negative version of the other (Research Hypothesis). For example: 

Null Hypothesis: There will not be an association between age and victimhood of crime 

Research Hypothesis: There will be an association between age and victimhood of crime

As you can see these two statements are mirroring each other as intended, you only need to simply add not to a null hypothesis to ensure its appropriateness. Essentially the null hypothesis is stating nothing will happen whilst the alternative hypothesis is saying ‘something’ will happen, though not stating exactly what. 

Two-tailed and One-tailed Hypotheses 

A two-tailed hypothesis simply predicts the independent variable will have an effect on the dependent variable, but the direction of the effect isn’t specified. In the example above it’s stated that there will be an association between age and victimhood of crime but not what it could be. 

A one-tailed, directional hypothesis predicts the nature of the effect of the independent variable on the dependent variable e.g. younger people are more likely to be a victim of crime. 

Independent and Dependent Variables 

In all of the above example hypotheses they’ve included two variables, the independent and dependent variable. You must know which is which to properly construct a hypothesis. 

An independent variable (IV) can be thought of as the variable not influenced by other variables being measured. These variables are typically thought of as being the cause and they influence the dependent variable. In the example above, age is the independent variable. 

A dependent variable (DV) is what you’re measuring in a statistical test and depends on other factors (such as the IV). It’s regarded as the outcome variable, showing the effect of the IV. In the above example, likelihood to be a victim of crime is the DV. 

There will be an association between age and victimhood of crime

It is sometimes possible for a variable to be an independent variable in one hypothesis and a dependent variable in another. It’s just important that you understand what you want to measure and the IV and DVs for each hypothesis and statistical test you do. 

Hypotheses for Test for Difference

So far, you’ve been shown how to construct a simple hypothesis for inferential tests but when you’re doing tests for difference your hypothesis will look slightly different. The process is the same with only one slight change of wording. When conducting a test for difference, your hypothesis must refer to difference in replacement of association. For example, 

Instead of simply writing ‘There will be an association between age and victimhood of crime’

You could write 

There will be an age difference in likelihood to be a victim of crime 

There will not be an age difference in likelihood to be a victim of crime. 

OR 

People’s likelihood to be a victim of crime will differ according to their age. 

People’s likelihood to be a victim of crime will not differ according to their age. 

The key thing here is the word difference, as you’re testing for difference. Furthermore, to reiterate the learning from this sprint, when creating hypotheses ensure you know which variable is your IV and DV and also which type of hypothesis you wish to produce, a one-tailed or two-tailed. 

Now, have a go at developing your own hypotheses for a Test for Difference using the variables below. 

IV: Gender

DV: Interest in politics 

Null Hypothesis: 

Research Hypothesis: 

IV: Social Class 

DV: Quality of life  

Null Hypothesis: 

Research Hypothesis: 

IV: Religion 

DV: Attendance at place of worship

Null Hypothesis: 

Research Hypothesis: