Tooth-Whitening Gum Smoking and drinking coffee have a tendency to stain teeth. In an effort to determine the ability of chewing gum to remove stains on teeth, researchers conducted an experiment in which 64 bovine incisors (teeth) were stained with natural pigments such as coffee for 10 days. Each tooth was randomly assigned to one of four treatments: gum A, gum B, gum C, or saliva. Each tooth group was placed into a device that simulated a human chewing gum. The temperature of the device was maintained at body temperature and the tooth was in the device for 20 minutes. The process was repeated six times (for a total of 120 minutes of chewing). The researcher conducting the experiment did not know which treatment was being applied to each experimental unit. Upon removing a tooth from the chewing apparatus, the color change was measured using a spectrophotometer. The percentage of stain removed by each treatment after 120 minutes is as follows: Gum A, 47.6%; Gum B, 45.2%, Gum C, 21.4%, Saliva, 2.1%. The researchers concluded that gums A and B removed significantly more stain than gum C or saliva. In addition, gum C removed significantly more stain than saliva.


g. State a factor that could affect the value of the response variable that is fixed at a set level.

Verified step by step guidance

1. Identify the response variable in the experiment, which is the percentage of stain removed from the teeth after treatment.
2. Understand that a factor is an explanatory variable that is manipulated or controlled in the experiment to observe its effect on the response variable.
3. Look for variables that are kept constant (fixed) during the experiment to ensure that any observed effect on the response variable is due to the treatments alone.
4. Note that the temperature of the chewing device is maintained at body temperature throughout the experiment, which is a controlled factor fixed at a set level.
5. Therefore, state that the temperature of the device is a factor fixed at a set level that could affect the value of the response variable.

Key Concepts

Response Variable

The response variable is the outcome measured in an experiment to assess the effect of treatments. In this study, it is the percentage of stain removed from the teeth, which quantifies the effectiveness of each gum or saliva in whitening. Understanding the response variable is crucial for interpreting results and comparing treatments.

Controlled Factors (Fixed Factors)

Controlled factors are variables kept constant to prevent them from influencing the response variable. For example, the temperature of the chewing device was fixed at body temperature to ensure consistent conditions across treatments. Identifying such factors helps isolate the effect of the treatments on stain removal.

Randomization and Blinding

Randomization assigns experimental units to treatments randomly to reduce bias, while blinding prevents researchers from knowing which treatment is applied, minimizing subjective influence. Both methods increase the validity and reliability of the experiment’s conclusions.