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The report "Comparative Study of Two Computer Mouse Designs" (Cornell Human Factors Laboratory Technical Report RP7992) included the following description of the subjects used in an experiment: Twenty-four Cornell University students and staff (12 males and 12 females) volunteered to participate in the study. Three groups of 4 men and 4 women were selected by their stature to represent the 5 th percentile (female \(152.1 \pm 0.3 \mathrm{~cm}\), male \(164.1 \pm 0.4 \mathrm{~cm}\) ), 50th percentile (female \(162.4 \pm 0.1 \mathrm{~cm}\), male \(174.1 \pm\) \(0.7 \mathrm{~cm}\) ), and 95 th percentile (female \(171.9 \pm 0.2 \mathrm{~cm}\), male \(185.7 \pm 0.6 \mathrm{~cm}\) ) ranges \(\ldots\) All subjects reported using their right hand to operate a computer mouse. This experimental design incorporated direct control and blocking. a. Are the potential effects of the extraneous variable stature (height) addressed by blocking or direct control? b. Whether the right or left hand is used to operate the mouse was considered to be an extraneous variable. Are the potential effects of this variable addressed by blocking or direct control?

Step by step solution

01

Identify and Understand Extraneous Variables

Extraneous variables are those factors which are not of direct interest in the experiment but can influence the experiment's outcome. In this case, the extraneous variables are the stature (height) and whether the right or left hand is used.

02

Understand Blocking and Direct Control

Blocking is a technique in experimental design to minimize or eliminate the effects of extraneous factors. We use another factor (blocking factor) that we believe can affect the outcome and divide it into blocks (groups). On the other hand, direct control involves eliminating the effect of extraneous variables by keeping them constant during the experiment.

03

Evaluate the Statute (Height) Variables

The stature (height) is divided into three groups: the 5th percentile, 50th percentile, and 95th percentile and then individuals were chosen from each group. This way, the effect of stature on the outcome is minimized. Therefore, blocking is applied for the stature (height) variable.

04

Evaluate the Hand Use Variables

In the experiment, all subjects are required to operate the computer mouse using their right hand. Hence, the extraneous variable of which hand is used has been kept constant – a characteristic of direct control.

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Key Concepts

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

Understanding Extraneous Variables

Extraneous variables are factors in an experiment that the researcher does not intend to study but which can influence the outcome. In the context of the cited study, stature (height) and the preferred hand for operating a computer mouse are the extraneous variables. To ensure the validity of the experiment's results, it's crucial to address these potential interferences.

For example, suppose an experiment is designed to compare the efficiency of two computer mouse designs. In that case, the height of participants or which hand they use may affect their performance, even though these factors are not the primary focus of the study. If not properly controlled, such variables can lead to incorrect conclusions being drawn from the experiment's data.

Blocking in Experimental Design

Blocking is a method of organizing experimental units into groups, or blocks, that are similar to each other. This technique is intended to reduce the confounding effects of extraneous variables within an experiment. By creating homogeneous blocks concerning certain characteristics, the variability within blocks is minimized, and thus, the experiment focuses on the differences caused by the treatments (or conditions) being tested.

In our exercise example, participants were blocked by stature into three categories representing different percentiles. This approach enabled the researchers to control for the variation in performance that could be attributed to height differences. It is important to note that each block should be tested under each experimental condition to ensure that the blocking is effective and the conclusions drawn from the experiment are reliable.

Direct Control in Experiments

Direct control is a straightforward approach where the researcher keeps extraneous variables constant throughout the experiment. This is done to eliminate the potential influence of these variables on the outcome. In the 'Comparative Study of Two Computer Mouse Designs', the researchers used direct control to keep hand dominance consistent among all participants by requiring them to use their right hand to operate the mouse.

This method simplifies the design and analysis of the experiment by holding certain factors steady, thus ruling them out as sources of variation in the results. While direct control is a powerful tool, it is not always feasible or ethical to control all extraneous variables, and in such cases, other methods, like blocking or randomization, might be utilized instead.