Therefore, in those cases where there is an odd number of scores, the calculation is straightforward; even numbers require some extra analysis to identify the median (Neuman, 2003). This measures if the easiest to use (Lomax, 2001) and can be used with nominal, ordinal, interval or ratio data (Neuman, 2003). The mode is simply the most common or frequently occurring number in such a series, but a distribution can have more than one mode (Neuman, 2003).

Sources: As indicated.

Conclusion

The research showed that the three common measures of central tendency are mean, median and mode, although other indexes also exist. The research also showed that the mode is the only appropriate measure of central tendency for nominal data, but that the median and mode are both appropriate for ordinal data (and conceptually the median fits the ordinal scale as both deal with ranked scores)....

In addition, all three measures of central tendency are appropriate for use with interval and ratio data.
References

Cai, J., Lo, J.J., & Watanabe, T. (2002). Intended treatments of arithmetic average in U.S. And Asian school mathematics textbooks. School Science and Mathematics, 102(8), 391.

Leavy, a.M. (2004). Indexing distributions of data: Preservice teachers' notions of representativeness. School Science and Mathematics, 104(3), 119.

Lomax, R.G. (2001). An introduction to statistical concepts for education and behavioral sciences. Mahwah, NJ: Lawrence Erlbaum Associates.

Neuman, W.L. (2003). Social research methods: Qualitative and quantitative approaches, 5th ed. New York: Allyn & Bacon.

Zevenbergen, R., Dole, S., & Wright, R.J. (2004). Teaching mathematics in primary schools. Crows Nest, N.S.W.: Allen & Unwin.