RM11 Threats and Nulls

what is a null effect?

the effect of the IV on the DV is not statistically significant

• below .05%

Why might a study find a null effect even if there is an effect?

weak manipulation

What is weak manipulation?

it is manipulating the IV across too narrow of a range

what is the ceiling effect?

a measurment limitation where to task is too easy or too narrow

What is the floor effect?

a measurement limitation where the task given is too difficult

what is internal validity?

the confidence that an experiments results show a true cause and effect relationship rather than being caused by other factors

what is a threat to internal validity?

perhaps an explanation to the results is different from what was thought

confound vs threat to internal validity

confound- a specific factor

threat to internal validity: a broader category

what is a maturation threat

change due to passage of time

what is a history threat?

result might be due to an external event rather than manipulation

what is regression to the mean?

a particularly high score means they will likely score lower the next, and vice versa

what is a testing threat?

improvement might reflect familiarity with the test

what is an attrition threat?

threat may reflect a difference due to dropout rate

• one group was at a weird time so the people who stayed were more commited

what is the selection effect?

subjects in one condition differ from others (esp ones that chose their groups such as classes)