WordNet

trace a line through or across; "cross your `t"
any affliction that causes great suffering; "that is his cross to bear"; "he bears his afflictions like a crown of thorns" (同)crown_of_thorns
a wooden structure consisting of an upright post with a transverse piece
extending or lying across; in a crosswise direction; at right angles to the long axis; "cross members should be all steel"; "from the transverse hall the stairway ascends gracefully"; "transversal vibrations"; "transverse colon" (同)transverse, transversal, thwartwise
to cover or extend over an area or time period; "Rivers traverse the valley floor", "The parking lot spans 3 acres"; "The novel spans three centuries" (同)traverse, span, sweep
fold so as to resemble a cross; "she crossed her legs"
meet and pass; "the trains crossed"
throughout an area; "he is known the world over"
(cricket) the division of play during which six balls are bowled at the batsman by one player from the other team from the same end of the pitch
throughout a period of time; "stay over the weekend" (同)o''er
at or to a point across intervening space etc.; "come over and see us some time"; "over there"
beyond the top or upper surface or edge; forward from an upright position; "a roof that hangs over";
(law) the determination of a persons innocence or guilt by due process of law; "he had a fair trial and the jury found him guilty"; "most of these complaints are settled before they go to trial"
trying something to find out about it; "a sample for ten days free trial"; "a trial of progesterone failed to relieve the pain" (同)trial_run, test, tryout
an annoying or frustrating or catastrophic event; "his mother-in-laws visits were a great trial for him"; "life is full of tribulations"; "a visitation of the plague" (同)tribulation, visitation
(sports) a preliminary competition to determine qualifications; "the trials for the semifinals began yesterday"
a path (often marked) where something (as a street or railroad) can be crossed to get from one side to the other (同)crosswalk, crossover
a voyage across a body of water (usually across the Atlantic Ocean)
traveling across
a point where two lines (paths or arcs etc.) intersect
placed crosswise; "spoken with a straight face but crossed fingers"; "crossed forks"; "seated with arms across"
(of a check) marked for deposit only as indicated by having two lines drawn across it

PrepTutorEJDIC

〈C〉(昔,罪人のはりつけの刑に用いた)『十字架』 / 《the C-》キリストがはりつけになった十字架;キリスト教の象徴としての十字架 / 〈C〉十字(キリスト教徒が右手で切る) / 〈C〉イエスのために耐える苦しみ,受難 / 〈C〉十字架像;(紋章などの)十字形 / 〈C〉キリスト教信仰;《集合的に》キリスト教徒 / 〈C〉十字記号(crisscross)(+または×) / 〈C〉《修飾語を伴って》十字勲章 / 《『the Cross』》南十字星(the Southern Cross) / 〈C〉(動物・植物の)(…間の)異種交配;雑種《+『between』+『名』+『and』+『名』》 / 〈C〉(ボクシングの)クロスパンチ / (信仰のしるしとして)〈人・自分〉‘に'『十字を切る』 / …'を'『交差させる』(『する』) / …‘に'『交差させて線を引く』;《英》〈小切手〉‘に'線引きする;…'を'横線(×印)をつけて消す《+『名』+『out』(『off』),+『out』(『off』)+『名』》 / …'を'『横切る』,横断する,渡る / 〈心〉'を'よぎる,‘に'ふと浮かぶ / …‘と'すれ違う,行き違う / …'を'妨げる,‘の'じゃまをする / …'を'交配する / 『交差する』,交わる / (…へ)『横切る』,渡る《+『over to』+『名』》 / すれ違いになる / 〈動物・植物が〉交配する,雑種になる / おこりっぽい,ふきげんな / (風が)反対の / 十文字に交差した,横切った
《上方の位置・場所》…『の上に』,を覆って;…に覆いかぶさって / 《移動を指す動詞とともに用いて》…『を越えて』 / 《状態を表す助詞とともに用いて》…を越えた向こうに / 《数詞を伴って》…『以上に』 / …『の一面に』,の至るところに / …『支配して』,より勝って / …『について』,に関して / …『しながら』に従事して / 《期間》…『の間ずっと』 / (電話・ラジオなど)『で』,によって / …に沿って,…を(along) / 『越えて』,渡って,向こうへ / 倒れて,ひっくり返って / 『終わって』,すんで / ひっくり返して / 『繰り返して』 / 『あふれて』;余って / 『終りまで』,ずっと,すっかり / 過度に / (クリケットで)乗判が交替を命じるまでの投球数
〈U〉〈C〉『裁判』,公判,審理 / 〈U〉〈C〉(…の)『試験』,ためし《+of+名》 / 〈C〉企て,試み;努力 / 〈C〉(忍耐・徳・信仰などをためす)試練,苦難 / 〈C〉困りもの,迷惑な(やっかいな)人(もの)
横断,横切ること;渡航 / 交差点,十字路;踏切,《英》横断歩道(《米》crosswalk),(河川・水路の)横断場所 / 異種交配(crossbreeding)
(十字形に)交差した / 十字を引いてある,線引きの

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/05/15 17:21:48」(JST)

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A crossover study, also referred to as a crossover trial, is a longitudinal study in which subjects receive a sequence of different treatments (or exposures). While crossover studies can be observational studies, many important crossover studies are controlled experiments, which are discussed in this article. Crossover designs are common for experiments in many scientific disciplines, for example psychology, education, pharmaceutical science, and medicine.

Randomized, controlled crossover experiments are especially important in health care. In a randomized clinical trial, the subjects are randomly assigned to different arms of the study which receive different treatments. When the randomized clinical trial is a repeated measures design, the same measures are collected multiple times for each subject. A crossover clinical trial is a repeated measures design in which each patient is randomly assigned to a sequence of treatments, including at least two treatments (of which one "treatment" may be a standard treatment or a placebo).

Nearly all crossover designs have "balance", which means that all subjects should receive the same number of treatments and that all subjects participate for the same number of periods. In most crossover trials, in fact, each subject receives all treatments.

Statisticians suggest that designs have four periods, a design which allows studies to be truncated to three periods while still enjoying greater efficiency than the two-period design.^[1]^[2] However, the two-period design is often taught in non-statistical textbooks, partly because of its simplicity.

Clinical trial protocol specifies the statistical analysis

The data are analyzed using the statistical method that was specified in the clinical trial protocol, which needs to have been approved by the appropriate institutional review boards and regulatory agencies before the trial could begin. Again, the clinical trial protocols specify the method of statistical analysis. Most clinical trials are analyzed using repeated-measurements anova (analysis of variance) or mixed models that include random effects.

In most longitudinal studies of human subjects, patients may withdraw from the trial or become "lost to follow-up" (due e.g. to moving abroad or to dying from another disease). There are statistical methods for dealing with such missing-data and "censoring" problems. An important method analyzes the data according to the principle of the intention to treat.

Advantages

A crossover study has two advantages over both a parallel study and a non-crossover longitudinal study. First, the influence of confounding covariates is reduced because each crossover patient serves as his or her own control^{[citation needed]}. In a non-crossover study, even randomized, it is often the case that different treatment-groups are found to be unbalanced on some covariates. In a controlled, randomized crossover designs, such imbalances are implausible (unless covariates were to change systematically during the study).

Second, optimal crossover designs are statistically efficient and so require fewer subjects than do non-crossover designs (even other repeated measures designs).

Optimal crossover designs are discussed in the graduate textbook by Jones and Kenward and in the review article by Stufken. Crossover designs are discussed along with more general repeated-measurements designs in the graduate textbook by Vonesh and Chinchilli.

Limitations and disadvantages

These studies are often done to improve the symptoms of patients with chronic conditions. For curative treatments or rapidly changing conditions, cross-over trials may be infeasible or unethical.

Crossover studies often have two problems:

First is the issue of "order" effects, because it is possible that the order in which treatments are administered may affect the outcome. An example might be a drug with many adverse effects given first, making patients taking a second, less harmful medicine, more sensitive to any adverse effect.

Second is the issue of "carry-over" between treatments, which confounds the estimates of the treatment effects. In practice, "carry-over" effects can be avoided with a sufficiently long "wash-out" period between treatments. However, planning for sufficiently long wash-out periods requires expert knowledge of the dynamics of the treatment, which is often unknown.

Also, there might be a "learning" effect. This is important where you have controls who are naive to the intended therapy. In such a case e.g. you cannot make a group (typically the group which learned the skill first) unlearn a skill such as yoga and then act as a control in the second phase of the study.

Notes

^ Vonesh & Chinchilli (1997)
^ Jones & Kenward (2003)

References

M. Bose and A. Dey (2009). Optimal Crossover Designs. World Scientific. ISBN 978-9812818423
D. E. Johnson (2010). Crossover experiments. WIREs Comp Stat, 2: 620-625. [1]
Jones, Byron; Kenward, Michael G. (2003). Design and Analysis of Cross-Over Trials (Second ed.). London: Chapman and Hall. ISBN 0412606402.
Najafi Mehdi, (2004). Statistical Questions in Evidence Based Medicine. New York: Oxford University Press. ISBN 0-19-262992-1
D. Raghavarao and L. Padgett (2014). Repeated Measurements and Cross-Over Designs. Wiley. ISBN 978-1-118-70925-2
D. A. Ratkowsky, M. A. Evans, and J. R. Alldredge (1992). Cross-Over Experiments: Design, Analysis, and Application. Marcel Dekker. ISBN 978-0824788926
Senn, S. (2002). Cross-Over Trials in Clinical Research, Second edition. Wiley. ISBN 978-0-471-49653-3
Stufken, J. (1996). "Optimal Crossover Designs". In Ghosh, S. and Rao, C. R. Design and Analysis of Experiments. Handbook of Statistics 13. North-Holland. pp. 63–90. ISBN 0-444-82061-2.
Vonesh, Edward F.; Chinchilli, Vernon G. (1997). "Crossover Experiments". Linear and Nonlinear Models for the Analysis of Repeated Measurements. London: Chapman and Hall. pp. 111–202. ISBN 0824782488.

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★リンクテーブル★

リンク元	「交差試験」「crossover study」「cross-over design」「cross-over study」「crossover trial」
関連記事	「cross」「trial」「crossing」「crossed」「tri」