Question

Design a controlled experiment to determine the effect of hot, dry air on head lice. In your experimental design, be sure to:

Answer 1

An experiment is carried out to answer a question. The hypothesis predicts what is expected to occur. Experimental and control groups are compared to analyze the results, supporting or not the hypothesis.

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BACKGROUND

When people are infested with head lice, it is recommended to wash their cloth and dry it with hot air over 53 or 54ºC for 5-30 minutes.

Head lice and eggs seem to die when exposed to those conditions by getting dehydrated.

SITUATION

We will assume that we work in a primary school and that students from the 3rth grade are being affected by this parasite.

We want to know if applying hot air to these students before entering the class will make a difference and help to control this problem.

So, we will propose an experiment to answer this question.

HYPOTHESIS

• A hypothesis is a conjecture.

• A researcher hypothesizes to predict what is going on or what is expected to occur.

• The hypothesis is a claim of how it works a relation between two or more variables.

• Usually, it is written in the present time.

Hypothesis ⇒ Applying hot air to students' heads kills the head lice that students are carrying.

To evaluate the effect of hot air, we need to keep control of as many other variables as possible.

To do so, we asked students' families not to use other treatments on students' heads and to bathe them daily.

In this way, we were sure that all students

• were equally affected by the parasite,
• took showers every day, and
• neither was using any other product that could affect the results.

Our population was the 3rth grade students ⇒ 64 children ⇒ 30 girls + 34 boys.

Before the experiment, we separated the 3rth grade into two groups.

• Group A ⇒ 32 students ⇒ 15 girls + 17 boys ⇒ Experimental group

• Group B ⇒ 32 students ⇒ 15 girls + 17 boys ⇒ Control group

→  Treatment

Each student from group A received hot air every day for one week before entering the class.

Hot air was 53ºC and was applied for 5 minutes.

→  Control

Each student from group B did not receive the treatment for one week before entering the class.

CONTROL GROUP

The control group is used to identify any other factors influencing the results obtained in the study, apart from the modified variables of the treatment.

Individuals of the control group are selected from the same population as the treatment group.

***  These two groups are identical in all aspects except for the independent variable, which changes in the treatment group but remains constant in the control group.  ***

• The control group is Group B.

• The only difference between the control and the experimental group is that the first one did not receive the treatment.

• Every other aspect was equal for both groups.

The only way the control group was treated differently from the experimental group was that the control group did not received the treatment, while the experimental group did.

RESULTS

After one week, groups were compared to see if the hot air was effective in killing head lice.

When comparing the control and the experimental group, we could see that students from group A were free of parasites.

Students from group B were still affected by the head lice.

CONCLUSION

The results support the hypothesis. Hot air turned to be a great treatment for lice control.

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