threats to internal validity

-

selection

if groups are not equal at the start of the experiment due to uneven random sampling

history

outside events or environment that affect the dv.

ct- history

confounding variables should be eliminated or kept constant.

maturation

growth or fatigue in experiment which can affect the dv.

ct- maturation

control grp

testing effect

first measurement effecting the next ones. You naturally do better after you have take the test once before.

ct- testing effect

control grp

instrumentation

when the instrument ur measuring dv with changes during dif runs. like getting tired

ct- instrumentation

standardize

regression to mean

extreme values being statistically better next time.

ct- regression

control grp with same starting point

experiment mortality

too many ppl drop out.

ct- experiment mortality

just dont make such experiments lmao

demand characteristics

participants accidentally guess the aim and change behavior to fit research expectation.

ct- demand characterstics

post experimental questionaires

experimenter bias

unintentionally or intentionally researcher effects study.

ct- experimenter bias

double blind- no one knows what's going on except a few researchers