CH14 internal and external validity and threats

internal validity

degree to which change measured can be attributed to the program itself

history

THREATS to internal:

unanticipated events happening between pre and post tests

maturation

THREATS to internal:

participants age between pre and post tests

testing

THREATS to internal:

programs become familiar with test formati

instrumentation

THREATS to internal:

•  change in measurement between pre and post tests

statistical regression

• THREATS to internal:

• extreme high and low scores change the average

selection

threat to internal

•  lack of randomization between experimental and comparison groups

attrition

threat to internal

participants drop out

interaction

threat to internal

__ between the control and experimental groups

external validity

• extent to which program can produce similar effects in other populations (generalizability)

social desirability

threat to external

when individuals give a particular response to try to impress or please the evaluator (give what you want to hear)

expectancy effect

threat to external

attitudes projected onto individuals cause them to act a certain way

hawthorne effect

threat to external

behavior change because they are aware of what is being studied

placebo effect

threat to external

belief in the treatment