Choosing sample distributions.
Sample distributions bear a paradoxical relationship to measurement.
On the one hand, they often simplify estimation or may even be required to make estimation possible. It is clearly preferable,whenever possible, to use estimation methods that do not require person or item distributions to be specified. The simplest sample distribution is the point distribution, hypothesizing a fixed effect. Many attitude surveys are conceptualized this way. When a population is thought to be represented by a central value, but individuals differ from that value in innumerable ways, each constituting a small amount, then the normal distribution is often chosen.