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28 CHAPTER 2 Experimental research

theory normally covers a larger scope and the establishment of a theory normally
requires a sequence of empirical studies. A concrete research hypothesis lays the
foundation of an experiment as well as the basis of statistical significance testing.

THEORY VS HYPOTHESIS

The differences between theories and hypotheses can be clearly demonstrated
by the extensive HCI research into Fitts' law (Fitts, 1954), one of the most
widely accepted theories in the HCI field. It states a general relationship
between movement time, navigation distance, and target size for pointing tasks
in an interface:
In movement tasks, the movement time increases as the movement
distance increases and the size of the target decreases. The movement
time has a log linear relationship with the movement distance and the
width of the target.
Fitts' law is a general theory that may apply to various kinds of pointing
devices. It is impossible to validate Fitts' law in a few experiments. Since Fitts'
law was proposed, hundreds of user studies have been conducted on various
pointing devices and tasks to validate and modify Fitts' law. The research
hypothesis of each of those studies is a much more focused statement covering
a small, testable application domain.
For example, Miniotas (2000) examined hypotheses about the performance
of two pointing devices: a mouse and an eye tracker. Movement time was
shorter for the mouse than for the eye tracker. Fitts' law predicted the navigation
time fairly well for both the mouse and the eye tracker, indicating the potential
to apply Fitts' law to technologies that do not rely on hand-based control.
Accot and Zhai (2003) investigated Fitts' law in the context of two-dimensional
targets. More recently, Bi et al. (2013) developed a FFitts law model that
expanded Fitts' law to finger touch input.

2.2.1 NULL HYPOTHESIS AND ALTERNATIVE HYPOTHESIS

An experiment normally has at least one null hypothesis and one alternative hypoth-
esis. A null hypothesis typically states that there is no difference between experi-
mental treatments. The alternative hypothesis is always a statement that is mutually
exclusive with the null hypothesis. The goal of an experiment is to find statistical
evidence to refute or nullify the null hypothesis in order to support the alternative hy-
pothesis (Rosenthal and Rosnow, 2008). Some experiments may have several pairs of
null hypotheses and alternative hypotheses. The characteristics of null and alternative
hypotheses can be better explained through the following hypothetical research case.
Suppose the developers of a website are trying to figure out whether to use a
pull-down menu or a pop-up menu in the home page of the website. The developers
decide to conduct an experiment to find out which menu design will allow the users