DISAIN EKSPERIMEN Sudrajat FMIPA UNMUL 2009

Isu pokok dalam disain eksperimen Manipulasi peubah bebas Seleksi peubah terikat Perlakuan terhadap subjek-subjek penelitian (unit-unit eksperimen ) Kontrol terhadap peubah luar

Manipulasi peubah bebas Dalam eksperimen klasik, peneliti mengukur kondisi peubah terikat pada subjek baik dari kelompok perlakuan maupun kelompok kontrol. Pada awal perlakuan kondisinya sama, kemudian dikelompokkan menjadi beberapa kelompok perlakuan. Pada akhir penelitian diukur kembali dan dianalisis untuk diperbandingkan antara kelompok kontrol dengan kelompok perlakuan tersebut.

Laboratorium vs Eksperimen Lapangan Artificial – Kurang Realis Sedikit peubah Extraneous Sangat terkontrol Biaya Murah Waktu pendek Subjek terkendali Natural – Sangat Realis Beberapa peubah ekstraneous Kurang terkontrol Biaya Mahal Waktu lama Subjek kurang terkendali

“ONE-SHOT” CASE STUDY T1 T2 T3 X O Dimana : X = Perlakuan O = Pengamatan

Manfaat utama disain riset? Secara ilmiah , disain riset belum tentu baik bagi semuanya Namun, Studi kasus dalam ilmu sosial menunjukkan adanya kontribusi yang lebih baik untuk mengembangkan berbagai disiplin ilmu dibandingkan dengan metode lain Pertama – banyak perintis bekerja dalam ilmu sosial yang melengkapi desainnya sebelum melakukan riset yang lebih canggih Kedua – peneliti selalu mengukur individu-individu dan untuk membedakan respon satu dengan lainnya diperlukan disain riset yang baik Ketiga – disain riset yang memerlukan pengontrolan canggih dibatasi untuk macam-macam keperluan yang berbeda

“ONE-GROUP” PRETEST - POSTTEST T1 T2 T3 O X O

“STATIC GROUP” COMPARISON T1 T2 T3 X O O

“PRETEST - POSTTEST” CONTROL GROUP DESIGN T1 T2 T3 Trt O X O Ctrl O O

Posttest-Only Control Group T1 T2 T3 O X O O

“SOLOMON” FOUR - GROUP DESIGN T1 T2 T3 O X O O O X O O

Disain eksperimen lebih kompleks Completely randomized designs ( CRD) Randomized block design ( RBD) Factorial design ( FD) Latin square design ( LSD)

Experimental Conditions Double Blind experiment – neither “observer” nor the “subjects” know whether the subject are in the treatment or control groups or receiving a placebo. Placebo effect – One experimental group is given the “treatment” that is being tested while another “treatment” group receives a “treatment” but one that is, by design, “benign” in its effect.

Extraneous Variables History Maturation Testing Instrumentation Selection Mortality

Extraneous Variables History – specific events in the environment between the before and after measurement that are beyond the experimenter’s control e.g. a major employer closes its plant in a test market area Maturation – subjects change during the course of the experiment e.g. subjects become tired

Extraneous variables (cont -2) Testing – the before measurement alerts subject to the nature of the experiment e.g. questionnaire about traditional role of women triggers enhanced awareness of women in the experiment Instrumentation – changes in measuring instrument result in response bias e.g. new questions about women are interpreted differently than earlier questions

Extraneous variables (cont -3) Selection – sample selection error occurs because of differential selection of comparison groups e.g. control and experimental groups are assigned self-selecting groups based on preference for soft drinks Mortality – sample attrition, some subjects withdraw from experiment e.g. subjects in one group of students withdraw from school

Control for Extraneous Variation Eliminate Extraneous Variables Hold Conditions Constant Randomization Matching Subjects

Demand Characteristics Design procedures that “hint” to subjects about the experimenter’s hypothesis Guinea Pig effect – when subjects exhibit behavior that they feel is expected of them Hawthorne effect – causes people to perform differently just because they know they are experimental subjects

Problems of Internal Validity Design History Maturation Testing Instrumentation Selection Mortality One shot design NR One group pre/post test design Static group design X ? Posttest Control Group only Pre/Post Control Group design Solomon Four Group design 0 = weakness X = factor controlled ? = possible concern NR = not relevant

Ethical Issues Harm “Unfair benefit” Privacy Confidentiality Deception Not using debriefing