Preference test

A preference test is an experiment in which animals are allowed free access to multiple environments which differ in one or more ways. Various aspects of the animal's behaviour can be measured with respect to the alternative environments, such as latency and frequency of entry, duration of time spent, range of activities observed, or relative consumption of a goal object in the environment. These measures can be recorded either by the experimenter or by motion detecting software. Strength of preference can be inferred by the magnitude of the difference in the response, but see "Advantages and disadvantages" below. Statistical testing is used to determine whether observed differences in such measures support the conclusion that preference or aversion has occurred. Prior to testing, the animals are usually given the opportunity to explore the environments to habituate and reduce the effects of novelty.

Preference tests can be used to test for preferences of only one characteristic of an environment, e.g. cage colour, or multiple characteristics e.g. a choice between hamster wheel, Habitrail tunnels or additional empty space for extended locomotion.

The simplest of preference tests offers a choice between two alternatives. This can be done by putting different goal boxes at the ends of the arms of a 'T' shaped maze, or having a chamber divided in into differing halves. A famous example of this simple method is an investigation of the preferences of chickens for different types of wire floor in battery cages. Two types of metal mesh flooring were being used in the 1950s; one type was a large, open mesh using thick wire, the other was a smaller mesh size but the wire was considerably thinner. A prestigious committee, the Brambell Committee, conducting an investigation into farm animal welfare concluded the thicker mesh should be used as this was likely to be more comfortable for the chickens. However, preference tests showed that chickens preferred the thinner wire. Photographs taken from under the cages showed that the thinner mesh offered more points of contact for the feet than the thick mesh, thereby spreading the load on the hens' feet and presumably feeling more comfortable to the birds.

The number of choices that can be offered is theoretically limitless for some preference tests, e.g., light intensity, cage size, food types; however, the number is often limited by experimental practicalities, current practice (e.g., animal caging systems) or costs. Furthermore, animals usually investigate all areas of the apparatus in a behaviour called "information gathering", even those with minor preference, so the more choices that are available may dilute the data on the dominant preference(s).

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