diseño cuasi-experimental

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Subject: Metodologa de la investigacin y estadstica I.Dr. Gregorio Gmez Hernndez

Group: 3CM8Castrejn Taboada XimenaBarroso Pineda Karla GuadalupeJimnez Garca Paloma del CarmenRoque Garcs EduardoTrinidad Silva Erick FranciscoVega Ovando Fabricio RafaelQuasi-Experimental Design.

Instituto Politcnico NacionalEscuela Superior de Medicina

What is the quasi-experimental design?

Quasi-experimental designThe term"quasi-experimento" refers to researchdesignornin which experimentalsubjects or groups of study subjects are not randomized.

Electionof groups, in which test a variable,without anykind of selectionorrandom or pre-selectionprocess.

Intact groupsSet of subjects that inquasi-experimentaldesignsarenot randomly assigned and are not matched, but were formed before the experiment

Example:Tomake an educational experiment, a class can be arbitrarily divided by alphabetic orderor by the disposition of the seats.Afterthis selection,theexperimentproceeds much like any other way, with a variable compared between different groups or while a period of time.

How useful is the quasi-experimental design?

Quasi-experimental DesignThismethodis veryuseful to measuresocial variables.The weaknesses inherent methodologydo not weakendata validity.

Advantages:Provides an approximationtothe random experiment when randomness is not possible.It isversatile.As random testing, quasi-experiments can be used to measure outcomes atpopulation level or of the program.

For example,astrictly experimentaldesignimpliesthat mothers were randomly assigned themtodrink alcohol.This willbeillegal because the possible damagethatthe study couldcause to the embryos.

Sowhatresearchers do is to ask peopleHow much alcohol did they ingested in their pregnancies and then assignthemto their respective groups.

DisadvantagesWithout a proper random assignment, statistics testsmay be insignificant.For example, theseexperimentaldesigndo not consider all pre-existing factors (such as for mothers: what madethemdrink alcohol or not), and do not recognize that the outside influences to the experiment might have affected the results.

A quasi-experiment built to analyze the effects of different educational programs in two children groups,for example, can generate results that show that a program is more effective than the other.

These results do not standuptoa rigorous statistic analysisbecause the researcheralsoneedto control other factors that may have affected the results.

One of the children groupsmaycouldhave been a little moresmart or a little more motivatedto.Without some form of ramdom pre-selection, is dificulttojudge the influence of these factors.

Classification.

Pre-experimental designsThey represent the basic modules from which the rest of the quasi-experimental designs are configured.

Designs single group, only postest.- Lacks control, so you can not draw causal inferences.Non-equivalent control group, only postest.- The results are not interpreted in causalities also without pretest we can not know whether the differences between groups (posttest) are due to differential treatment or selection.A single group, pretest + postest.- useful to suggest hypotheses for future research.

QUASI EXPERIMENTAL DESIGNS.

With a control group.Control group equivalente.- The allocation rule groups is not known because you work with already formed groups, despite this, who investigates try to select groups as possible equivalents.

Cohortes.- design Cohort: Group of persons belonging to an institution subject over a period of time similar circumstances. It helps to study how a particular event affects a group (experimental cohort) and compares it with another that did not live the event (control group).

Without control group.Sometimes it is not possible to have a control group, for practical or ethical reasons, as in the medical treatment.They have less power to justify causal inferences designs with control groups.

Design withdrawal treatment.- With the treatment withdrawal, who is investigating, tries to create conditions to exercise the function of the control group.Repeated treatment design: is available with an only group in which the research staff introduce, remove and reinsert the treatment, at different times.

Interrupted time series.Results are observed before and during treatment, making periodic records.For their analysis you have to know when treatment is introduced.If it is effective, subsequent observations will show a change in the series.It is often used in:Social studies.Educational studies.Health studies.Evaluationprograms

BibliographyManterola, Carlos, & Otzen, Tamara. (2015). Estudios Experimentales 2 Parte: Estudios Cuasi-Experimentales.International Journal of Morphology,33(1), 382-387.https://dx.doi.org/10.4067/S0717-95022015000100060