# BIO 500 W7 Discussion Question 2

*BIO 500 W7 Discussion Question 2*

*BIO 500 W7 Discussion Question 2*

Explain why computing a variance of several numbers is like analyzing their differences.

An **interaction variable** or **interaction feature** is a variable constructed from an original set of variables to try to represent either all of the interaction present or some part of it. In exploratory statistical analyses it is common to use products of original variables as the basis of testing whether interaction is present with the possibility of substituting other more realistic interaction variables at a later stage. When there are more than two explanatory variables, several interaction variables are constructed, with pairwise-products representing pairwise-interactions and higher order products representing higher order interactions.

Thus, for a response *Y* and two variables *x*_{1} and *x*_{2} an *additive* model would be:

- {\displaystyle Y=c+ax_{1}+bx_{2}+{\text{error}}\,}

In contrast to this,

- {\displaystyle Y=c+ax_{1}+bx_{2}+d(x_{1}\times x_{2})+{\text{error}}\,}

is an example of a model with an *interaction* between variables *x*_{1} and *x*_{2} (“error” refers to the random variable whose value is that by which *Y* differs from the expected value of *Y*; see errors and residuals in statistics). Often, models are presented without the interaction term {\displaystyle d(x_{1}\times x_{2})}, but this confounds the main effect and interaction effect (i.e., without specifying the interaction term, it is possible that any main effect found is actually due to an interaction).

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In statistics, an **interaction** may arise when considering the relationship among three or more variables, and describes a situation in which the effect of one causal variable on an outcome depends on the state of a second causal variable (that is, when effects of the two causes are not additive).^{[1]}^{[2]} Although commonly thought of in terms of causal relationships, the concept of an interaction can also describe non-causal associations. Interactions are often considered in the context of regression analyses or factorial experiments.

The presence of interactions can have important implications for the interpretation of statistical models. If two variables of interest interact, the relationship between each of the interacting variables and a third “dependent variable” depends on the value of the other interacting variable. In practice, this makes it more difficult to predict the consequences of changing the value of a variable, particularly if the variables it interacts with are hard to measure or difficult to control.

The notion of “interaction” is closely related to that of moderation that is common in social and health science research: the interaction between an explanatory variable and an environmental variable suggests that the effect of the explanatory variable has been moderated or modified by the environmental variable.^{}

## Participation for MSN

### Threaded Discussion Guiding Principles

The ideas and beliefs underpinning the threaded discussions (TDs) guide students through engaging dialogues as they achieve the desired learning outcomes/competencies associated with their course in a manner that empowers them to organize, integrate, apply and critically appraise their knowledge to their selected field of practice. The use of TDs provides students with opportunities to contribute level-appropriate knowledge and experience to the topic in a safe, caring, and fluid environment that models professional and social interaction. The TD’s ebb and flow is based upon the composition of student and faculty interaction in the quest for relevant scholarship. Participation in the TDs generates opportunities for students to actively engage in the written ideas of others by carefully reading, researching, reflecting, and responding to the contributions of their peers and course faculty. TDs foster the development of members into a community of learners as they share ideas and inquiries, consider perspectives that may be different from their own, and integrate knowledge from other disciplines.

### Participation Guidelines

Each weekly threaded discussion is worth up to 25 points. Students must post a **minimum** of two times in each graded thread. The two posts in each individual thread must be on separate days. The student **must provide an answer to each graded thread topic** posted by the course instructor, by Wednesday, 11:59 p.m. MT, of each week. If the student does not provide an answer to each graded thread topic (not a response to a student peer) before the Wednesday deadline, 5 points are deducted for each discussion thread in which late entry occurs (up to a 10-point deduction for that week). Subsequent posts, including essential responses to peers, must occur by the Sunday deadline, 11:59 p.m. MT of each week.

**Direct Quotes**

Good writing calls for the limited use of direct quotes. Direct quotes in Threaded Discussions are to be limited to one short quotation (not to exceed 15 words). The quote must add substantively to the discussion. Points will be deducted under the Grammar, Syntax, APA category.

### Grading Rubric Guidelines

**NOTE:** To receive credit for a week’s discussion, students may begin posting no earlier than the Sunday immediately before each week opens. Unless otherwise specified, access to most weeks begins on Sunday at 12:01 a.m. MT, and that week’s assignments are due by the next Sunday by 11:59 p.m. MT. Week 8 opens at 12:01 a.m. MT Sunday and closes at 11:59 p.m. MT Wednesday. Any assignments and all discussion requirements must be completed by 11:59 p.m. MT Wednesday of the eighth week.