1what is the standard error of measurments ?
a measure of how much measured test scores are spread around a "true" score
2what **assumptions** does SEM have ?
1. varince of measurment error = all individuals taking test
2. measurment error is normally distributed
1. mean = M = o , standard deviation = SDe
3. standard deviation of measurment error is a measure of the expected deviation of X relative to T
3what is the SEM formula ?
4what does SEM stand for ?
SEM = standard error of measurment
5what does SDx stand for ?
SDx = standard deviation of X in sample
6what does rxx stand for ?
rxx = (estimated) reliability of the test
7what is SEM in perfectly reliable test ?
r will be 1
8whi r= 1 is a perfectly reliable test ?
squareroot of 0 = 0
SEM = 0
9what is a CI ?
CI = intterval in which with a certain percentage of certainty lies the individual's true score
10what range score for CI are there ?
range of scores within which true score lies
68 90 95 99%
11how do we get from SEM to CI?
1. administer test and determine score
2. calulate standard measuremnt error SDe of the test
3. claculate CI
12how to conduct **step 1**?
complete questionnaire by participant or parent
we need the score itself
13how to conduct **step 2**?
use the formula to calculate
we need reliability rxx of test
we need SDx of the test
14what is the 68 % CI interval ?
Xi +/ _ 1 x SDe
15what is the 90 % CI interval ?
Xi + 1.65 x SDe
16what is the 95 % CI interval ?
**Xi + 1.96 x SDe**
17what is the 95 % CI interval ?
Xi + 3 x SDe
18how do we conduct step 3?
calculate the lower limit and upper limit of the score
19what confidence interval is usually used?
95%
lower limit : Xi _ 1.96 x SDe
upper limit : Xi + 1.96 x SDe
20whan do we use SE diff ?
when we want to find the difference in 2 scores
21what do we need in order to find SEdiff?
M and SD
22what do we use in order to calculate difference?
SE diff
23what are the formula used ?
24how do we use SEdiff to calcualte CI for difference scores?
1. determine difference between scores
2. calculate SEdiff
3. calculate CI 95% of difference score
25how do we determine difference between scores ?
initial _ actual
26how do we calculate SE diff ?
1. use reliability rxx of both tests and SDx of both tests
2. use measurment error SDe of both tests
27how do we calcualte CI 95% of difference score ?
28when is there a difference ?
if the CI does not include zero , there is a real difference
29what could be another approach ?
calcualte confidence interval around 0
why ? know which range difference scores could actually be 0
30what are the steps of calculating the CI around 0 ?
1. no difference , use 0
2. calcualte SEdiff (with formula)
3. calualte CI interval
31when is there no actual difference if we calulate CI around 0 ?
*scores in that range imply no actual difference
32how do we calcualte differecne if we test with different instrument?
1. chack the difference between scores
2. use the formula based on what info we have
3. calculate CI
4. coclude : does it include 0?
33how do we find an acceptable level of reliability in terms of context?
what is the "price " of a wrong decision ?
how much on an influence does the test have ?
34how do we find the acceptable level of reliability in terms of level ?
individual : needs higher reliability
groups / reserch : requires less reliability
35what is the interval of reliability for an important decision ?
Good : more than .90
sufficinet : between .80 and .90
insufficint : less than 80
36what is the interval of reliability for a less important decision ?
good : more than .80
sufficint : between .70 and .80
insufficint : less than .70
37what is the interval of reliability for a group level decision ?
good : less than .70
sufficint : between .60 and .70
insufficint : less than .60
38what alternatives of CTT are there ?
IRT : item response theroy
39what is IRT ?
measurment error depends on test score
reliability items may be distinguished between individuals
charachterisitcs of items
1. difficulty
2. discrimination index
3. measure fir unformative function
we test the "test construcution "