The correct choice is “independent variable.” The independent variable is changed in order to observe the changes, if any, that it has on the dependent variable or variables. The dependent variable is defined as the variable that changes in response to the independent variable.

The distance that any point is from the mean is known as the standard deviation. When looking at a normal distribution, the mean is the middle or arithmetic average of the set and the deviation measures the spread of the data points from this central tendency.

Ordinal data is used when variables that have an inherent natural order, such as the collegiate class structure: freshman, sophomore, junior, senior.  One must complete every level in order to transcend to the next. Nominal data deals with variables such as religion that do not have an inherent natural order. Interval data deals with things like temperature. Last, ratio data would deal with things like time. 

A normal distribution is asymptotic because it approaches a curve closely. It is unimodal because of its singular mode, and it is symmetric because both sides are mirror images of each other. There are other kinds of distributions like skewed distributions that are unimodal, asymptotic, and asymmetrical. These descriptions can vary depending on the shape of the distribution. 

A parameter measures a population—the whole group that is being considered. A statistic represents a measure of a sample—a subset of the group that is being considered. For example, if you were conducting a study on Spanish people in your university, then the population would be all of the Spanish people at your university. A sample could be all of the Spanish people in one of your classes. 

The mean of a Z-score is zero. This means that the score is the same as the mean. A positive or negative Z-score would show that it is above or below the mean and by how many standard deviations. 

The distribution is positive because its tail goes to toward the right. If it were negative, the tail would go toward the Y-axis, or the left. If a distribution's tail is longer on either side, then it is not a normal distribution. It is not symmetrical and would be classified as a skewed distribution. 

A correlational study looks at the relationship between two or more variables. For example, the relationship between test scores in math and history classes. It does not try to find a cause and effect between the variables, and the researcher does not manipulate the variables. The researcher is simply trying to see if they possess a relationship or correlation. 

This symbol represents a command to find the sum of two or more numbers. This symbol is the Greek letter 'E' and is used in a variety of equations. It is called Epsilon.