Randomized experiment: Difference between revisions

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[[Image:Flowchart of Phases of Parallel Randomized Trial - Modified from CONSORT 2010.png|thumb|250px|right|Flowchart of four phases (enrollment, intervention allocation, follow-up, and data analysis) of a parallel randomized trial of two groups, modified from the [[Consolidated Standards of Reporting Trials|CONSORT 2010 Statement]]<ref name="Schulz-2010">{{Cite journal | author = Schulz KF, Altman DG, Moher D; for the CONSORT Group | title = CONSORT 2010 Statement: updated guidelines for reporting parallel group randomised trials | journal = BMJ | volume = 340 | pages = c332 | year = 2010 | doi = 10.1136/bmj.c332 | url = http://www.bmj.com/cgi/content/full/340/mar23_1/c332 | pmid = 20332509 | pmc = 2844940 }}</ref>]] In [[scientific method|science]], '''randomized experiments''' are the [[experiment]]s that allow the greatest reliability and validity of statistical estimates of treatment effects. Randomization-based inference is especially important in [[experimental design]] and in [[survey sampling]].

In [[scientific method|science]], '''randomized experiments''' are the [[experiment]]s that allow the greatest reliability and validity of statistical estimates of treatment effects. Randomization-based inference is especially important in [[experimental design]] and in [[survey sampling]].

== Overview ==

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| url = http://www.exp-platform.com/Documents/2015%20Online%20Controlled%20Experiments_EncyclopediaOfMLDM.pdf

}}</ref> to create a feedback loop.<ref name="surveyarticle">{{cite journal

| coauthorsauthors = Kohavi, Ron; Longbotham, Roger; Sommerfield, Dan; Henne, Randal M.

| last = Kohavi

| first = Ron

| coauthors = Longbotham, Roger; Sommerfield, Dan; Henne, Randal M.

| title = Controlled experiments on the web: survey and practical guide

| journal = Data Mining and Knowledge Discovery

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{{main|History of experiments}}

The earliest controlled experiment appears to have been suggested in the Old Testament's Book of Daniel. King Nebuchadnezzar proposed that some Israelites eat "a daily amount of food and wine from the king's table." Daniel preferred a vegetarian diet, but the official was concerned that the king would "see you looking worse than the other young men your age? The king would then have my head because of you." Daniel then proposed the following controlled experiment: "Test your servants for ten days. Give us nothing but vegetables to eat and water to drink. Then compare our appearance with that of the young men who eat the royal food, and treat your servants in accordance with what you see". (Daniel 1, 12– 13).<ref>{{cite journal

| last = KohaviNeuhauser

Daniel then proposed the following controlled experiment: "Test your servants for ten days. Give us nothing but vegetables to eat and water to drink. Then compare our appearance with that of the young men who eat the royal food, and treat your servants in accordance with what you see” (Daniel 1, 12– 13).<ref>{{cite journal

| lastfirst = NeuhauserD

|author2=Diaz, M

| first = D

| title = Daniel: using the Bible to teach quality improvement methods

|author2=Diaz, M

| journal = Quality and Safety in Health Care 2004

| title = Daniel: using the Bible to teach quality improvement methods

| volume = 13

| journal = Quality and Safety in Health Care 2004

| volumeissue = 132

| issuepages = 2153–155

| pagesyear = 153–1552004

| url = http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1743807/pdf/v013p00153.pdf

| year = 2004

| doi = 10.1136/qshc.2003.009480

| url = http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1743807/pdf/v013p00153.pdf

| pmid=15069225

| doi = 10.1136/qshc.2003.009480

| pmc=1743807

| pmid=15069225

| pmc=1743807

}}</ref><ref>{{cite book

| last = Angrist

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</ref>

Randomized experiments were institutionalized in psychology and education in the late eighteen-hundreds, following the invention of randomized experiments by [[Charles Sanders Peirce|C. S. Peirce]].<ref>{{cite journal| author=[[Charles Sanders Peirce]] and [[Joseph Jastrow]]| year=1885|title=On Small Differences in Sensation| journal=Memoirs of the National Academy of Sciences|volume=3|pages=73–83|url=http://psychclassics.yorku.ca/Peirce/small-diffs.htm}} http://psychclassics.yorku.ca/Peirce/small-diffs.htm</ref><ref>{{cite journal| doi=10.1086/354775| first=Ian |last=Hacking| authorlink=Ian Hacking | title=Telepathy: Origins of Randomization in Experimental Design|journal=[[Isis (journal)| Isis]]| issue=3| volume=79| date=September 1988 |pages=427–451| mr = 1013489| jstor=234674}}</ref><ref>{{cite journal| doi=10.1086/444032|author=[[Stephen M. Stigler]]|title=A Historical View of Statistical Concepts in Psychology and Educational Research| journal=American Journal of Education| volume=101| issue=1| date=November 1992|pages=60–70}}</ref><ref>{{cite journal|doi=10.1086/383850|author=Trudy Dehue|title=Deception, Efficiency, and Random Groups: Psychology and the Gradual Origination of the Random Group Design|journal=[[Isis (journal)|Isis]]| volume=88| issue=4| date=December 1997| pages=653–673|pmid=9519574}}</ref>

Outside of psychology and education, randomized experiments were popularized by [[R.A. Fisher]] in his book [[Statistical Methods for Research Workers]], which also introduced additional principles of experimental design.

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==Empirical evidence that randomization makes a difference==

Empirically differences between randomized and non-randomized studies,<ref>{{cite journal| doi=10.1002/14651858.MR000034.pub2|author=Anglemyer A, Horvath HT, Bero L| title=Healthcare outcomes assessed with observational study designs compared with those assessed in randomized trials| journal=Cochrane Database Syst Rev|date=April 2014| pmid=24782322| volume=4| pages=MR000034}}</ref> and between adequately and inadequately randomized trials have been difficult to detect. <ref>{{cite journal| doi=10.1002/14651858.MR000012.pub3 | vauthors=Odgaard-Jensen J, Vist G, etal |title=Randomisation to protect against selection bias in healthcare trials.| journal=Cochrane Database Syst Rev| date=April 2011|pmid=21491415|pages=MR000012}}</ref><ref>{{cite journal| doi=10.1186/1745-6215-15-480|author=Howick J, Mebius A|title=In search of justification for the unpredictability paradox| journal=Trials| year=2014| volume=15| pmid=25490908| pages=480}}</ref>

.<ref>{{cite journal|doi=10.1186/1745-6215-15-480|author=Howick J, Mebius A|title=In search of justification for the unpredictability paradox|journal=Trials|year=2014|volume=15|pmid=25490908|pages=480}}</ref>

==See also==

*[[A/B testing]]

*[[Random assignment]]

*[[Randomized block design]]

*[[Randomized controlled trial]]

*[[Random assignment]]

*[[A/B testing]]

==References==

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}}

* {{cite journal|doi=10.1086/354775|first=Ian |last=Hacking| authorlink=Ian Hacking | title=Telepathy: Origins of Randomization in Experimental Design|journal=[[Isis (journal)|Isis]]|issue=3|volume=79|date=September 1988 |pages=427–451| mr = 1013489| jstor=234674}}

*{{cite book| |last1=Hinkelmann | first1=Klaus | last2=Kempthorne | first2=Oscar | year=2008 | title=Design and Analysis of Experiments, Volume I: Introduction to Experimental Design | url=https://books.google.com/?id=T3wWj2kVYZgC&printsec=frontcover | edition=Second| publisher=[http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0471727563.html Wiley] | isbn=978-0-471-72756-9 |mr=2363107 |authorlink2=Oscar Kempthorne}}

* {{cite book| last=Kempthorne|first=Oscar |chapter=Intervention experiments, randomization and inference|title=Current Issues in Statistical Inference&mdash;Essays in Honor of D. Basu | editor=Malay Ghosh and Pramod K. Pathak | pages=13&ndash;31 | publisher=Institute for Mathematical Statistics |___location=Hayward, CA | url=http://projecteuclid.org/euclid.lnms/1215458836 | doi=10.1214/lnms/1215458836 | mr=1194407|authorlink=Oscar Kempthorne}}