four validities

• construct
• external
• satistical
• internal

variable anything that varies / changes in measurement

• variables can be measured; be observed and recorded

variables can be manipulated

• controls assignment levels (called an independent variable)
• not all experiments have an ID

constant

• a potential variable that is kept at a single level / keep steady across multiple conditions

measured: rating / feeling of belonging manipulated: the intervention program constant: the program itself throughout the colleges + the timeframe of asking the student's rating

some variables can only be measured and not manipulated

• not possible (age)
• not practical (neighborhoods)
• unethical (drugs in pregnancy)

conceptual variable - constructs (i.e happiness)

operational variable - concrete definition; specific procedure to measure concept