Hypothesis writing
Students often struggle with writing good hypothesis. Students must be able to write two types of hypotheses: a null
hypothesis, which states that there will be no relationship between the independent and dependent variable, and
the alternative hypothesis (aka the research hypothesis) which clearly predicts the relationship between the
independent and dependent variable.
The purpose of this activity is to have students practice writing null and research hypotheses. There is a worksheet
attached.
Hypothesis writing worksheet
Hypotheses
The first thing that students need to understand before they can begin their internal assessment is the concept of a
hypothesis. The experimental method is based on hypothesis testing. Inferential testing asks the researcher to
choose between a null and an alternative (research) hypothesis. You are actually calculating the probability of the
result occurring if the null hypothesis is true.
The first step is to state the null hypothesis. The null hypothesis assumes that there will be no significant difference
for a given population under two different conditions. For example:
H0: Individuals show no significant difference in the mean number of words that students recall from a list of
40 unrelated words when in a quiet room than when listening to music.
The IV and the DV are clearly stated. The IV is whether the individual is in a quiet room or listening to music. The
DV is recalling words from a list of 40 unrelated words. First, notice that the variables are operationalized - that is,
they are very clearly defined for us so we know exactly what is being manipulated and what is being measured. Also
notice that the null hypothesis states that there will be no significant difference. This is important because we are not
saying that the mean recall must be exactly the same in order to retain the null hypothesis - it is only important that
there not be a "significant difference" - that is, a large enough difference to say that the results were not due to
chance.
The alternative hypothesis is your guess about what will happen. For the above experiment, the researcher
hypothesis could be:
H1: Participants will memorize more words from a list of 40 unrelated words when they are in a quiet room
than when listening to the radio.
Notice that there is a clear guess as to the outcome of the experiment.
What if we find that they remember fewer words? If that is true, then the alternative hypothesis is not supported, but
neither is the null hypothesis also not supported because there is a difference in the number of words memorized. If
the null is rejected because there is no correct alternative hypothesis, the experiment is technically invalid. It is not
possible to change any hypothesis retrospectively.
The way to solve this is to state a two-tailed hypothesis instead of a one-tailed hypothesis. A two-tailed hypothesis
does not state the direction:
H1: There will be a difference in the number of words that participants will memorize from a list of 40 unrelated
words when they are in a quiet room than when listening to the radio.
The two-tailed test gets you away from the trap of getting results that do not accept your alternative hypothesis but
clearly are significant. It is not acceptable practice to change your hypothesis after you get your results to match
your findings. A two-tailed hypothesis is usually done in psychology to investigate a question. A one-tailed test is
often used to test the reliability of a study's findings.