Chapter 2: Misconceptions When people read, hear, or prepare research summaries, they sometimes have misconceptions about what is or isn't "sound practice" regarding the collection, analysis, and interpretation of data. Here are some of these common (and dangerous) misconceptions associated with descriptive statistics. The mean is superior to either the median or the mode. If a mean and a standard deviation are cited for a group of data, those two indices "say it all." Data that approximate the normal distribution are superior to data that are skewed. Frequency distributions, bargraphs, stem-and-leaf displays, and box plots are so elementary that they don't belong in sophisticated research summaries. A standard deviation indicates how far a typical score will deviate from the mean. The highest score in a group will always be about six standard deviations higher than the lowest score in that group. If drawn correctly, a normal curve must resemble a bell. Standard scores (such as z-scores or T-scores) are computed by researchers only when the original data are normally distributed. The only three measures of central tendency are the mean, the median, and the mode. The word "average" is synonymous with the word "mean." The normal curve is curved most at the points of inflection (i.e., above the baseline points of z = +1.0 and z = -1.0) If the male test scores have a SD = 10 and the female test scores have a SD = 20, the SD for the combined group of males and females will be equal to 15.