1. A researcher conducts an experiment comparing four treatment conditions with

Question

1. A researcher conducts an experiment comparing four treatment conditions with 20 scores in each treatment condition (so the dataset includes a total of 80 scores).

a. If the experiment used an independent-measures design, how many subjects would need to participate?

b. If the experiment used a repeated-measures design, how many subjects would need to participate?

c. The researcher would like to minimize the influence of pre-existing individual differences between subjects (such as age, gender, or personality) on the results. Should the researcher use an independent-measures design or a repeated-measures design? Why?

Explanation / Answer

1)

a) If there are independent measures design the subjects needed will be 20 for each treatment , thus 4 treatment will need 20 * 4 = 80 . We will need 80 subjects for independent measures design . As we are considering independent individual for each treatment and for each score .

b) It the experiment has repeated measures , we can consider same 20 subjects for all four treatments . Therefore in this case subjects will be 20.

c) When researcher would like to minimize the influence of pre-existing individual differences between subjects such as age , gender or personality it is alwayz better to consider independent measures design . Thus consdering different subjects for each treatment and taking 20 different scores in each treatment . We will prefer this design because the same individual participating in all the four treatments can increase the biasness . In research design samples should always be independent of each other and they can be independent if we donot use sample repeatedly for every treatment .

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