To see why OLS is logical, imagine a regression line running 6 units below one data point and 6 units above another point; it is 6 units away from the two points, on average. Now suppose a second line runs 10 units below one data point and 2 units above another point; it is also 6 units away from the two points, on average. But if we square the distances involved, we get different results: 6 2 + 6 2 = 72 in the first case, and 10 2 + 2 2 = 104 in the second case. So the first line yields the lower figure — the “least squares” — and is a more consistent reduction of the distance from the data points. (Additional methods, besides OLS, can find the best line for more complex forms of regression analysis.)
In turn, the typical distance between the line and all the points (sometimes called the “standard error”) indicates whether the regression analysis has captured a relationship that is strong or weak. The closer a line is to the data points, overall, the stronger the relationship.
Regression analysis, again, establishes a correlation between phenomena. But as the saying goes, correlation is not causation. Even a line that fits the data points closely may not say something definitive about causality. Perhaps some students do succeed in French class because they study hard. Or perhaps those students benefit from better natural linguistic abilities, and they merely enjoy studying more, but do not especially benefit from it. Perhaps there would be a stronger correlation between test scores and the total time students had spent hearing French spoken before they ever entered this particular class. The tale that emerges from good data may not be the whole story.
So it still takes critical thinking and careful studies to locate meaningful cause-and-effect relationships in the world. But at a minimum, regression analysis helps establish the existence of connections that call for closer investigation.
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March 16, 2010
I hope this kind of thing ("Explained")becomes a regular feature. Even if we learned about things like regression in school, it is easy to forget if you don't use it regularly.
July 15, 2011
Yes, this is written with exceptional clarity. Do continue this feature by this author.
31 Oct 2013
Recently I had a read of
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by Lukas Smith ( nike air air max sandals
) about the use of the DELETE method when building RESTful services. I wanted to get my thoughts down on this. Mostly to help myself, but if it helps you determine a better approach, then great.
I'm nowhere near qualified enough to preach, so this is by no means a "you should do it this way / my way is correct post", just food for thought. Besides, there are probably more questions here than answers.
So, Lukas highlights an interesting point ( which appears to still be debate ), about the correct status code to return upon the successful deletion of a resource, and whether that code should ever change for subsequent requests. In general debate is:
So first off let's try to determine what idempotence is in respect to HTTP and how it applied to REST services. According to RFC 2616 (section 9.1.2) :
"the side-effects of N > 0 identical requests is the same as for a single request"
So if you send a request with exactly the same input, the side-effects will be identical. But...
Initially I found the term "side-effects" threw me. It wasn't clear whether this side-effect needs to be considered for the server or the client. In respect to the DELETE method the initial request (which performs the deletion of a resource) will have completely different side effects to subsequent requests (that won't). Does this mean DELETE is NOT idempotent? Maybe. Maybe it means what it says, or maybe we're misunderstanding something.
If you were to look up the term idempotence you'll notice in other applications of the word it refers to the "resulting" effect of an operation. Given an input, the same output will always be returned. As a mathematical example: An operation of adding 10 (to any number) is idempotent. The result (per given input) will always be the same. So does idempotence mean identical results or identical operation? I honestly can't find a definitive distinction anywhere. According to wikipedia "it means that the modified state remains the same after the first call". So again, this has no bearing on the operational effect, just the end result. So let's extend our example:
This operation will always return the same result (per input), but it may randomly idle for 5 seconds, meaning the side effects are different. According to Wikipedia this operation IS idempotent . The state of $number will always be the same for every call. According to RFC 2616 this operation is NOT idempotent as the operational side effects can vary. I think it would also be correct to say that any operation that needs to check external state before it can determine a result is also not idempotent. Be it the current time, a file in a file system or a record in a database.Contact: Subjects:
As Directorof Research Services and head of the Liaison Librarian Program, I work extensively with students and faculty to help them access the resources they need for teaching, learning, and research. I also serve as the Liaison Librarian for the College of Education and the Departments of Art and TheatreDance. I provide library instruction for undergraduate and graduate classes, provide in-person research consultations, and provide collections support in my liaisonareas.
I hold an M.L.S. from the University of North Texas and an M.A. in Theatre from the University of Colorado at Boulder. I am currently pursuing a Ph.D. in Educational Leadership from the University of Nevada, Reno.
Beisler, M., Medaille, A. (2016).
How do students get help with research assignments? Using drawings to understand students’ help seeking behavior
Journal of Academic Librarianship, 42
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Brown, N. E., Bussert, K., Hattwig, D., Medaille, A. (2016). Visual literacy for libraries: A practical, standards-based guide . Chicago: ALA Editions.
Blithe, S. J., Carrera, W., Medaille, A. (2015). Stories of service-learning: Guidelines for increasing student engagement with digital storytelling . Journal of Library Innovation, 6 (1), 60–74.
Medaille, A., Beisler, M., Radniecki, T., Ressel, M., Slater, H., Cooper, D., Foster, N. F. (2015). Exploring group study at the University of Nevada, Reno . New York: Ithaka S+R.
Ennis, D., Medaille, A., Lambert, T., Kelley, R., Harris, F. C., Jr. (2013). A comparison of academic libraries: An analysis using a self-organizing map . Performance Measurement and Metrics, 14 (2), 118–131. https://doi.org/10.1108/PMM-07-2012-0026
Hattwig, D., Bussert, K., Medaille, A., Burgess, J. (2013). Visual literacy standards in higher education: New opportunities for libraries and student learning . portal: Libraries and the Academy, 13 (1), 61–89.
Medaille, A., Shannon, A. W. (2012). Co-teaching relationships among librarians and other information professionals . Collaborative Librarianship, 4 (4), 132–148.
More than 20,000 Americans died from synthetic drug overdoses in 2016. That represents 31 percent of all drug overdose deaths, a surging percentage in recent years — more than double the number from 2015 .
A bill called the
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aims to combat on the growing epidemic of synthetic drug deaths. But would it give Jeff Sessions too much power?
There are more than 400 known types of synthetic — or “artificial” — drugs, which mimic the effects of substances including cocaine and ecstasy. They’ve largely begun to flood the market in recent years, this decade in particular.
The Drug Enforcement Administration (DEA), quite simply, cannot keep up. The bureaucratic process they follow when determining whether a drug should be put on the banned substances list, and what corresponding penalties should go along with each drug, can take several years of evaluation.
Advocates say the U.S. doesn’t have years.What the billdoes
The bill outlaws 13 different synthetic drugs of the most pernicious varieties, by creating a new “schedule” (a term for “categorization”) to the list of banned substances on the Controlled Substances Act. The list of the 13 drugs can be seen in section 2, subsection 3B .
It also creates a process by which substances can be added — whether temporarily or permanently — in as little as 30 days after first being identified, rather than the years it can potentially take under current law. The lead House sponsor relayed a story during a committee hearing of a constituent from his New York district who died from overdosing on a synthetic drug which nonetheless remained legal for four years afterward .
Although the bill creates penalties for trafficking and distribution of these synthetic drugs, what the bill does not do is criminalize mere possession of such synthetic drugs . In this way, they intend to go after the proliferators rather than the users.
The bill was introduced in the House in June 2017 by Rep. John Katko (R-NY24), labelled as H.R. 2851 . It was introduced in the Senate that same month by Sen. Chuck Grassley (R-IA), labelled as S. 1327 .