TOPIC 3: Hypothesis Testing
Watch this video clip in the "Talking Head" explain the null and alterative hypothesis.
Comment on what has been said.
copyright  September, 2008  
What is a Hypothesis?
You can also state Research Questions in the form of a "hypothesis". Hypothesis is singular and hypotheses is plural. A hypothesis is a tentative statement that explains a particular phenomenon which is testable. The key word is "testable". Refer to the following statements:

1.    Juvenile delinquents tend to be from low socio-economic families.
2.    Children who attend kindergarten are more likely to have higher reading scores.
3.    The discovery method of teaching may enhance the creative thinking skills of students.
4.    Children with tuition tend to perform better in mathematics.

All theses are examples of hypotheses.  However, these statements are not partcularly useful because because words such as "may", "tend to" and "more likely". Using these words tentative words does not suggest how you would go about proving it. To solve this problem, hypotheses are used. A hypothesis should consist of the following attributes:
       Your car will not start. You put forward the hypothesis that "the car that does not start because there is no petrol". You check the fuel gauge to either reject or accept the hypothesis. If you find there is petrol, you reject the hypothesis.
Next, you hypothesise that "the car did not start because the spark plugs are dirty". You check the spark plugs to determine if they are dirty and accept or reject the hypothesis accordingly.
  • Rewrite the four hypotheses using the formalised style shown. Ensure that each hypothesis has all the attributes mentioned above
  • Write two more original hypotheses of your own using this form.
Gender variable / Independent variable:  Male and Female
Critical Thinking Test / Dependent Variable
States a Relationship
Examine the above hypothesis. It has all the attributes listed above:

The null hypothesis is a hypothesis (or hunch) about the population. It represents a theory that has been put forward because it is believed to be true. The word "null" means nothing or zero. So, a null hypothesis states that 'nothing happened'. For example, there is no difference between males and females in critical thinking skills or there is no relationship between socio-economic status and academic performance. Such a hypothesis is denoted with the symbol  "Ho:".  In other words you are saying,
Say for example you conduct an experiment to test the effectiveness of the discovery method in learning science compared to the lecture method. You select a random sample of 30 students for the discovery method group and 30 students for the lecture method group.
Based on your sample you hypothesise that there are no differences in science achievement between students in the discovery method group and students in the lecture method group. In other words, you make the claim that there are no differences in science scores between the two groups in the population. This is represented by the following two types null hypotheses with the following notation or Ho:

          (i.e. µ1 ≠ µ2).

  • What is the meaning of a null hypothesis?
  • What do you mean when you "reject" the null hypothesis?
  • What is the alternative hypothesis?
  • What do you mean when you "accept" the alternative hypothesis?
         Ho:  µ1 = µ2                    OR             Ho:  µ1 - µ2 = 0 
In other words, you are saying that:
Alternative Hypothesis
The Alternative Hypothesis (H1) is the opposite of the Null Hypothesis. For example, the alternative hypothesis for the study discussed earlier is that there is a difference in science scores between the discovery method group and the lecture method group represented by the following notation:                    
Ha:  µ1 ≠ µ2        
Ha:  µ1 > µ2

Ha:  µ1 < µ2
When you have completed this  chapter you will be able to:

  • Explain the difference between the null and alternative hypothesis and their use in research
  • Differentiate between Type 1 and Type 2 error
  • Explain when the two-tailed and one-tailed test is used
The null hypothesis is often the reverse of what the researcher actually believes in and it is put  forward to allow the data to contradict it
[You may find it strange but that's the way it is!]