BIO 550 Does association imply causation?

DQ1 Does association imply causation? Why or why not?

DQ2 Are weak associations indicative of a noncausal relationship? Select two other peers postings and debate their rationale.

Most studies include multiple response variables, and the dependencies among them are often of great interest. For example, we may wish to know whether the levels of mRNA and the matching protein vary together in a tissue, or whether increasing levels of one metabolite are associated with changed levAre weak associations indicative of a noncausal relationship? Select two other peers postings and debate their rationale.els of another. This month we begin a series of columns about relationships between variables (or features of a system), beginning with how pairwise dependencies can be characterized using correlation.

Two variables are independent when the value of one gives no information about the value of the other. For variables X and Y, we can express independence by saying that the chance of measuring any one of the possible values of X is unaffected by the value of Y, and vice versa, or by using conditional probability, P(X|Y) = P(X). For example, successive tosses of a coin are independent—for a fair coin, P(H) = 0.5 regardless of the outcome of the previous toss, because a toss does not alter the properties of the coin. In contrast, if a system is changed by observation, measurements may become associated or, equivalently, dependent. Cards drawn without replacement are not independent; when a red card is drawn, the probability of drawing a black card increases, because now there are fewer red cards.

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Association should not be confused with causality; if X causes Y, then the two are associated (dependent). However, associations can BIO 550 Does association imply causation arise between variables in the presence (i.e., X causes Y) and absence (i.e., they have a common cause) of a causal relationship, as we’ve seen in the context of Bayesian networks¹. As an example, suppose we observe that people who daily drink more than 4 cups of coffee have a decreased chance of developing skin cancer. This does not necessarily mean that coffee confers resistance to cancer; one alternative explanation would be that people who drink a lot of coffee work indoors for long hours and thus have little exposure to the sun, a known risk. If this is the case, then the number of hours spent outdoors is a confounding variable—a cause common to both observations. In such a situation, a direct causal link cannot be inferred; the association merely suggests a hypothesis, such as a common cause, but does not offer proof. In addition, when many variables in complex systems are studied, spurious associations can arise. Thus, association does not imply causation.

In everyday language, dependence, association and correlation are used interchangeably. Technically, however, association is synonymous with dependence and is different from correlation (Fig. 1a). Association is a very general relationship: one variable provides information about another. Correlation is more specific: two variables are correlated when they display an increasing or decreasing trend. For example, in an increasing trend, observing that X > μ_X implies that it is more likely that Y > μ_Y. Because not all associations are correlations, and because causality, as discussed above, can be connected only to association, we cannot equate correlation with causality in either direction.

Grid View

	Excellent	Good	Fair	Poor
Main Posting	45 (45%) – 50 (50%) Answers all parts of the discussion question(s) expectations with reflective critical analysis and synthesis of knowledge gained from the course readings for the module and current credible sources. Supported by at least three current, credible sources. Written clearly and concisely with no grammatical or spelling errors and fully adheres to current APA manual writing rules and style.	40 (40%) – 44 (44%) Responds to the discussion question(s) and is reflective with critical analysis and synthesis of knowledge gained from the course readings for the module. At least 75% of post has exceptional depth and breadth. Supported by at least three credible sources. Written clearly and concisely with one or no grammatical or spelling errors and fully adheres to current APA manual writing rules and style.	35 (35%) – 39 (39%) Responds to some of the discussion question(s). One or two criteria are not addressed or are superficially addressed. Is somewhat lacking reflection and critical analysis and synthesis. Somewhat represents knowledge gained from the course readings for the module. Post is cited with two credible sources. Written somewhat concisely; may contain more than two spelling or grammatical errors. Contains some APA formatting errors.	0 (0%) – 34 (34%) Does not respond to the discussion question(s) adequately. Lacks depth or superficially addresses criteria. Lacks reflection and critical analysis and synthesis. Does not represent knowledge gained from the course readings for the module. Contains only one or no credible sources. Not written clearly or concisely. Contains more than two spelling or grammatical errors. Does not adhere to current APA manual writing rules and style.
Main Post: Timeliness	10 (10%) – 10 (10%) Posts main post by day 3.	0 (0%) – 0 (0%)	0 (0%) – 0 (0%)	0 (0%) – 0 (0%) Does not post by day 3.
First Response	17 (17%) – 18 (18%) Response exhibits synthesis, critical thinking, and application to practice settings. Responds fully to questions posed by faculty. Provides clear, concise opinions and ideas that are supported by at least two scholarly sources. Demonstrates synthesis and understanding of learning objectives. Communication is professional and respectful to colleagues. Responses to faculty questions are fully answered, if posed. Response is effectively written in standard, edited English.	15 (15%) – 16 (16%) Response exhibits critical thinking and application to practice settings. Communication is professional and respectful to colleagues. Responses to faculty questions are answered, if posed. Provides clear, concise opinions and ideas that are supported by two or more credible sources. Response is effectively written in standard, edited English.	13 (13%) – 14 (14%) Response is on topic and may have some depth. Responses posted in the discussion may lack effective professional communication. Responses to faculty questions are somewhat answered, if posed. Response may lack clear, concise opinions and ideas, and a few or no credible sources are cited.	0 (0%) – 12 (12%) Response may not be on topic and lacks depth. Responses posted in the discussion lack effective professional communication. Responses to faculty questions are missing. No credible sources are cited.
Second Response	16 (16%) – 17 (17%) Response exhibits synthesis, critical thinking, and application to practice settings. Responds fully to questions posed by faculty. Provides clear, concise opinions and ideas that are supported by at least two scholarly sources. Demonstrates synthesis and understanding of learning objectives. Communication is professional and respectful to colleagues. Responses to faculty questions are fully answered, if posed. Response is effectively written in standard, edited English.	14 (14%) – 15 (15%) Response exhibits critical thinking and application to practice settings. Communication is professional and respectful to colleagues. Responses to faculty questions are answered, if posed. Provides clear, concise opinions and ideas that are supported by two or more credible sources. Response is effectively written in standard, edited English.	12 (12%) – 13 (13%) Response is on topic and may have some depth. Responses posted in the discussion may lack effective professional communication. Responses to faculty questions are somewhat answered, if posed. Response may lack clear, concise opinions and ideas, and a few or no credible sources are cited.	0 (0%) – 11 (11%) Response may not be on topic and lacks depth. Responses posted in the discussion lack effective professional communication. Responses to faculty questions are missing. No credible sources are cited.
Participation	5 (5%) – 5 (5%) Meets requirements for participation by posting on three different days.	0 (0%) – 0 (0%)	0 (0%) – 0 (0%)	0 (0%) – 0 (0%) Does not meet requirements for participation by posting on 3 different days.
Total Points: 100