MEASURES OF CENTRAL TENDENCY

• Whenever you collect data, you end up with a group of scoreson one or more variables. If you take the scores on one variable and arrange them in order from lowest to highest, what you get is a distribution of scores.
• The "mean" is simply the arithmetic average of a distribution of scores, and researchers like it because it provides a single, simpler number that gives a rough summary of the distribution.
• The "median" is the score in the distribution that marks the 50th percentile.
• The "mode" is the least used of the measures of csntral tendency because it provides the least amount of information.
• Two different symbols are needed because it is important to distinguish between a statistic that applies to a sample and a parameter that applies to a population.
• To find the median of a distribution, you need to first arrange all of the scores in the distribution in order, from smallest to largest.
• The distribution has multiple mode and is called multimodal.
• In the messy world of social sciences, however, the scores from a sample on a given variable are often not normally distributed.
• When the scores in a distribution tend to bunch up at one end of the distribution and there are a few scores at the other end, the distribution is said to be skewed.
• When working with a skewed distribution, the mean, media, and mode are usually all at different points.
• If the tail of the distribution were pulled out toward the higher end, this would have been a positevely skewed distribution.
• The mean of a distribution can be affected by scores that are unusually large or small for a distribution, sometimes called outliers.