1. Design of studies

Controlled experiments

• Study units, population, sample, variable, response, factors
• treatment, treatment group, control group, placebo.
• blind and double-blind studies, randomized study, stratified experiment

Observational Studies

• Controlling for variables, confounding factors, stratified study
• Distinguishing between Controlled Experiments and Observational Studies

Sample Surveys

• Sampling unit, population, parameter, sample, statistic
• Sources of bias: selection bias, nonresponse bias, response bias,
• A large sample does not protect against selection bias
• Sampling procedures --- simple random sample, stratified sample, quota sample
  --- describe, identify, strengths and weaknesses

2. Displaying data

• qualitative vs. quantitative, discrete vs. continuous
• Categorical variables: nominal, ordinal; ordered categorical, interval scale

• Understanding histograms: the shape tells us the relative counts/percent in different intervals
  --- Area represents the percent in specified intervals
  --- Scale on the vertical axis are percent per horizontal-axis unit.
• Forms of histogram display: bars of equal/different widths, back-to-back, stacked
  Pie charts, Bar charts, Stem-and-leaf diagrams