Experimental Design Research Methods

Independent variable (treatment) The independent variable is manipulated by the experimenter. Examples of independent variables include: Fitness levels, type of practice, contextual interference, strategy for imagery, music … Controls Active and assigned variables Between subjects and within subjects (repeated measure) variables

Within Subjects/Repeated Measure Counterbalancing, using a Latin Square Design When an experiment has multiple treatments, conditions, or tasks they can be counterbalanced across subjects by using a Latin Square Design. In using a Latin Square Design all orders are not represented; however , all conditions are represented at least once in each position of the order to observe the effects of position and to control for practice, boredom, fatigue…. Order 1 A B C Order 2 Order 3

Standardization Validity Reliability Objectivity Sensitivity Dependent Variable The dependent variable is the variable measured by the experimenter (e.g., reaction time, heart rate, VO2Max, a survey score) Concerns Standardization Validity Reliability Objectivity Sensitivity

Statistical Testing Differences Associations Relationships Categorical Independent Variables; Continuous Dependent Variables Differences T-test ANOVA Categorical Independent Variables; Categorical Dependent Variables Associations Chi squared Continuous Independent Variables; Continuous Dependent Variables Relationships Correlation Regression

Null Directional Alternative Writing Hypotheses Null Directional Alternative

Null Hypotheses State the null hypothesis when no literature exists State the null hypothesis when the literature is controversial or equivocal State when there is no theoretical direction

Writing Null Hypotheses Stated in the null form Independent variable (insert name) will not affect dependent variable (insert name). Independent variable (insert name) will not associate with the dependent variable (insert name). Independent variable (insert name) will not relate to the dependent variable (insert name).

Directional Hypothesis State when the literature provides a clear direction State when the literature is unequivocal State when good theoretical support exists

Writing Directional Hypotheses Independent variable (levels A and B) will affect the dependent variable such that A will be significantly different than B. Independent variable (levels A and B) will associate with the dependent variable such that B will be significantly associated with B in specific ways. Independent variable (levels A and B) will relate to the dependent variable such that B will be significantly and positively (or negatively) related to B.

Writing Problems How does the independent variable affect the dependent variable? How does the independent variable associate with the dependent variable? How does the independent variable relate to the dependent variable?

Main Effects and Interaction effects Also you might need to consider interaction and main effects? What if you have two independent variables? Main effects include the analysis of a single independent variable and all of its levels. Interaction effects include the analysis of more than one independent variables and the interaction of all of their levels.

Interaction of Two Independent Variables (3*2 factorial design) Gender Male Female Overall Mean Type of Practice Massed Distributed Control

Pure Experimental Designs Randomized groups Design Pretest-Posttest Randomized-Groups Design Solomon Four-Group Design

Randomized-Groups Design T O1 O2

Pretest-Posttest Randomized-Groups Design

Solomon Four-Group Design T O2 O3 O4 O5 O6