Research Design

Time of Data Collection Longitudinal Longitudinal –Panel study –Trend study –Cohort study Cross-sectional Cross-sectional

Selecting the Sample Sample Size Sample Size –The bigger the better  Degree of accuracy?—Margin of Error (we will come back to this)

Control Manipulation Manipulation Elimination or inclusion Elimination or inclusion Statistical controls Statistical controls Randomization Randomization –Random selection –Random assignment

Validity Internal Validity Internal Validity External validity External validity

Threats to Internal Validity Other variables are causing the results History History Maturation Maturation Testing Testing Instrumentation Instrumentation Regression toward the mean Regression toward the mean Selection Selection Mortality Mortality Diffusion Diffusion Compensatory rivalry Compensatory rivalry Resentful Demoralization Resentful Demoralization

Threats to External Validity Depends on the Target Population Treatment-Attribute interaction Treatment-Attribute interaction Treatment-Setting interaction Treatment-Setting interaction Multiple Treatment Interference Multiple Treatment Interference Pretest Sensitization Pretest Sensitization Posttest Sensitization Posttest Sensitization

Research Should… Answer questions Answer questions Control Control Test hypotheses Test hypotheses Have clear variables Have clear variables –Independent, dependent, and control Dictates the type of analyses used Dictates the type of analyses used

Max-Min-Con Principle Max: Maximize systematic variance Max: Maximize systematic variance –Treatment effect Min: Minimize error variance Min: Minimize error variance Con: Control extraneous variables Con: Control extraneous variables

Classes of Designs Experimental Experimental –Manipulation and randomization Quasi-experimental Quasi-experimental –Manipulation but not randomization Non-experimental Non-experimental –No manipulation, no randomization

Quasi-Experimental Design Example Nonequivalent Control Group Nonequivalent Control Group –Difference score method –Pretest/posttest design with only one group receiving the treatment O X O O O Dashed line means the groups aren’t randomly assigned (quasi-experimental)

Non-Experimental Design ( Correlational research or survey research) Predictive or Explanatory Predictive or Explanatory Inferences made in the opposite direction Inferences made in the opposite direction –Attempt to detect or uncover the independent variables Probability sampling is very important in non-experimental designs Probability sampling is very important in non-experimental designs Control through subject selection and statistical adjustment Control through subject selection and statistical adjustment