91Ó°ÊÓ

An ad for Crest Whitestrips Premium claims that the strips will whiten teeth in 7 days and the results will last for 12 months. A researcher who wishes to test this claim studies 20 sets of identical twins. Within each set of twins, one is randomly selected to use Crest Whitestrips Premium in addition to regular brushing and flossing, while the other just brushes and flosses. Whiteness of teeth is measured at the beginning of the study, after 7 days, and every month thereafter for 12 months. (a) What type of experimental design is this? (b) What is the response variable in this experiment? (c) What are the treatments? (d) What are other factors (controlled or uncontrolled) that could affect the response variable? (e) What might be an advantage of using identical twins as subjects in this experiment?

Step by step solution

01

- Identify the Experimental Design

The experiment involves comparing the effectiveness of an additional whitening treatment (Crest Whitestrips Premium) on a sample where each twin in a pair is treated differently. This setup, where one twin uses the strips and the other does not, characterizes a matched-pairs design.

02

- Identify the Response Variable

The response variable is the whiteness of the teeth. It is measured at the beginning of the study, after 7 days, and every month thereafter for 12 months to observe the effects of the treatment.

03

- Specify the Treatments

The treatments in this experiment include using Crest Whitestrips Premium in addition to regular brushing and flossing versus just regular brushing and flossing without the use of the strips.

04

- Identify Other Factors

Other factors that could affect the response variable may include the participants' diet, frequency of brushing and flossing, genetic predispositions, and overall oral hygiene habits. These factors should be controlled or accounted for as much as possible.

05

- Explain the Advantage of Using Identical Twins

Using identical twins as subjects controls for genetic and environmental factors since they share the same genetics and likely similar habits. This helps isolate the effect of Crest Whitestrips Premium from other variables, leading to more reliable results.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

matched-pairs design

This experiment is a perfect example of a matched-pairs design. In a matched-pairs design, subjects are paired based on similarities. Often, this includes characteristics like age, gender, or other relevant factors. Here, identical twins are used to form the pairs. One twin uses Crest Whitestrips Premium, while the other does not. Each twin is compared directly with their sibling.
This design helps in minimizing the differences between the pairs, making it easier to attribute changes in the response variable to the treatment.

response variable

The response variable is what researchers measure to see the effect of treatments. In this experiment, the response variable is the 'whiteness of teeth.' It is measured at the beginning of the study, after 7 days, and every month for 12 months.
Measuring at multiple points helps in understanding how long the effects last and if they change over time. Monitoring the whiteness more frequently captures short-term changes, while monthly checks track longer-term effects.

treatment groups

In any experiment, treatment groups are essential to understanding how different treatments affect the response variable. Here, there are two treatment groups:

• The first group uses Crest Whitestrips Premium in addition to regular brushing and flossing.
• The second group only brushes and flosses, without using any whitening strips.

Comparing these groups shows the added effect (if any) of Crest Whitestrips Premium.
It's crucial to apply the treatments consistently to get accurate results.

controlled factors

Controlled factors are those that researchers try to keep the same across the experiment to ensure that any changes in the response variable are due to the treatment alone. Factors to control in this experiment may include:

• Diet: Certain foods can stain teeth.
• Brushing and flossing frequency: Consistent oral hygiene practices are needed.
• Genetic predispositions: Since identical twins are used, this is inherently controlled.
• Overall oral hygiene habits: Adherence to a consistent routine is crucial.

By controlling these factors, researchers minimize external influences, making it easier to observe the genuine impact of Crest Whitestrips Premium.

identical twins experiment

Using identical twins in experiments offers significant advantages. Identical twins share the same genetic makeup and usually have similar habits and environments. This dramatically reduces the variability due to genetic and environmental factors.

• More accurate results: Researchers can attribute differences in the response variable more confidently to the treatment.
• Control for genetic factors: Genetic predispositions that might affect tooth whiteness are controlled.
• Consistency: Twins likely have similar diet and hygiene habits, helping to isolate the treatment's effect.

Overall, using identical twins makes for highly reliable and precise experimental results.