Statistik at TU München

a observational study that collects information after the events took place

numerical variable that can only take numerical values with jumps

a numerical variable that can take any numerical value

a variable that can take categories

a categorical variable without natural ordering

A categorical variable with natural ordering

• collecting data in a way that does not directly interfere with how the data arise
• can provide evidence of naturally occurring association between variables
• does not show a casual connection

• checks for casual connection between variables
• controlls circumstances

• a single case (may be representative or not) to reject or justify a statement 

a variable that is correlated with explanatory and response variable but not observed in the observational study

study that observes while events unfold

• divide population into strata
  • similar cases belong to the same stratum
• use second sampling method within each stratum
• Advantage:
  • useful when cases in each stratum are similar
• Disadvantage:
  • analyzing data is more complex