Internal Validity

A researcher conducted a study to determine the effectiveness of the Collaborative Method, Lecture Method and Computer-Assisted Method in teaching mathematics to 16-year old students in a secondary school. She used a quasi-experimental design for her study and selected sample and divided them into three groups as shown in the table below.



Collaborative Method


Lecture Method


Computer-Assisted Method


At the end of the experiment which lasted for 10 weeks, all subjects were tested on their mathematics performance and the scores were compared.

  1. Why do you think the researcher selected a quasi-experimental design and not a true design?

  2. State TWO (2) null hypotheses for the study.

  3. Discuss FOUR (4) threats to the internal validity of the experiment.

  4. Explain any TWO (2) techniques that the researcher could use to ensure the three groups are equivalent in ability.

  5. In order to reject the null hypothesis, it is necessary to analyse the data statistically. Explain.

Part C (10%) – 3 pages

Attitude Toward Recycling of Waste

  •  Design a FIVE (5) item attitude scale to measure the above. [include it in your answer]
  •  Briefly describe how you would ensure that the attitude scale measures what it is supposed to measure.

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