(no subject)

[John run]

I was reading a research article that reported the results of a paired-samples t-test. The author reported the significance (t(125) = 64.24, p<.0001) and then reported the effect size of.71. Is the correlation coefficient reported in the output generated by SPSS the effect size or was the effect size a separate calculation?
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[Richard Ristow]

At 10:25 PM 2/8/2008, John run wrote:

>I was reading a research article that reported the results of a
>paired-samples t-test. The author reported the significance (t(125)
>= 64.24, p<.0001) and then reported the effect size of.71. Is the
>correlation coefficient reported in the output generated by SPSS the
>effect size or was the effect size a separate calculation?

The effect size is almost certainly the estimated mean difference of
the two variables. In the following output (draft output) from SPSS's
T-TEST, it's the Mean under 'Paired Differences' in the Paired
Samples Test. (The code to generate this output is at the end of this posting.)


Paired Samples Statistics
|----|--|------|---|--------------|---------------|
|    |  |Mean  |N  |Std. Deviation|Std. Error Mean|
|----|--|------|---|--------------|---------------|
|Pair|X1|5.9225|125|4.51181       |.40355         |
|1   |--|------|---|--------------|---------------|
|    |X2|6.6787|125|4.60598       |.41197         |
|----|--|------|---|--------------|---------------|

Paired Samples Correlations
|------|-------|---|-----------|----|
|      |       |N  |Correlation|Sig.|
|------|-------|---|-----------|----|
|Pair 1|X1 & X2|125|.976       |.000|
|------|-------|---|-----------|----|

Paired Samples Test
|------|-----|-------------------------------------|------|---|-------|
|      |     |Paired Differences                   |t     |df |Sig.   |
|      |     |------|-------|-------|--------------|      |   |(two-  |
|      |     |Mean  |Std.   |Std.   |95% Confidence|      |   |tailed)|
|      |     |      |Dev.   |Error  |Interval of   |      |   |       |
|      |     |      |       |of Mean|the Difference|      |   |       |
|      |     |      |       |       |------|-------|------|---|-------|
|      |     |      |       |       |Lower |Upper  |      |   |       |
|------|-----|------|-------|-------|------|-------|------|---|-------|
|Pair 1|X1-X2|-.7561|1.00418|.08982 |-.9339|-.5783 |-8.419|124|.000   |
|------|-----|------|-------|-------|------|-------|------|---|-------|

===================================
APPENDIX: Test data and T-test code
===================================
SET RNG = MT       /* 'Mersenne twister' random number generator  */ .
SET MTINDEX = 6820 /*  Providence, RI telephone book              */ .


NEW FILE.
INPUT PROGRAM.
.  NUMERIC CaseID (N3).
.  LEAVE   CaseID.
.  NUMERIC X1 X2  (F5.2).
.  LOOP    CaseID = 1 TO 125.
.     COMPUTE #Common = RV.NORMAL(0.1*CaseID,3).
.     COMPUTE #Delta  = RV.NORMAL(0.71,1).
.     COMPUTE X1      = #Common - #Delta/2.
.     COMPUTE X2      = #Common + #Delta/2.
.     END CASE.
.  END LOOP.
.  END FILE.
END INPUT PROGRAM.

T-TEST
   PAIRS = X1  WITH X2 (PAIRED)
   /CRITERIA = CI(.95)
   /MISSING = ANALYSIS.

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[Kornbrot, Diana]

Agree. See my post last week
diana


On 11/2/08 06:23, "Richard Ristow" <[hidden email]> wrote:

> At 10:25 PM 2/8/2008, John run wrote:
>
>> >I was reading a research article that reported the results of a
>> >paired-samples t-test. The author reported the significance (t(125)
>> >= 64.24, p<.0001) and then reported the effect size of.71. Is the
>> >correlation coefficient reported in the output generated by SPSS the
>> >effect size or was the effect size a separate calculation?
>
> The effect size is almost certainly the estimated mean difference of
> the two variables. In the following output (draft output) from SPSS's
> T-TEST, it's the Mean under 'Paired Differences' in the Paired
> Samples Test. (The code to generate this output is at the end of this
> posting.)
>
>
> Paired Samples Statistics
> |----|--|------|---|--------------|---------------|
> |    |  |Mean  |N  |Std. Deviation|Std. Error Mean|
> |----|--|------|---|--------------|---------------|
> |Pair|X1|5.9225|125|4.51181       |.40355         |
> |1   |--|------|---|--------------|---------------|
> |    |X2|6.6787|125|4.60598       |.41197         |
> |----|--|------|---|--------------|---------------|
>
> Paired Samples Correlations
> |------|-------|---|-----------|----|
> |      |       |N  |Correlation|Sig.|
> |------|-------|---|-----------|----|
> |Pair 1|X1 & X2|125|.976       |.000|
> |------|-------|---|-----------|----|
>
> Paired Samples Test
> |------|-----|-------------------------------------|------|---|-------|
> |      |     |Paired Differences                   |t     |df |Sig.   |
> |      |     |------|-------|-------|--------------|      |   |(two-  |
> |      |     |Mean  |Std.   |Std.   |95% Confidence|      |   |tailed)|
> |      |     |      |Dev.   |Error  |Interval of   |      |   |       |
> |      |     |      |       |of Mean|the Difference|      |   |       |
> |      |     |      |       |       |------|-------|------|---|-------|
> |      |     |      |       |       |Lower |Upper  |      |   |       |
> |------|-----|------|-------|-------|------|-------|------|---|-------|
> |Pair 1|X1-X2|-.7561|1.00418|.08982 |-.9339|-.5783 |-8.419|124|.000   |
> |------|-----|------|-------|-------|------|-------|------|---|-------|
>
> ===================================
> APPENDIX: Test data and T-test code
> ===================================
> SET RNG = MT       /* 'Mersenne twister' random number generator  */ .
> SET MTINDEX = 6820 /*  Providence, RI telephone book              */ .
>
>
> NEW FILE.
> INPUT PROGRAM.
> .  NUMERIC CaseID (N3).
> .  LEAVE   CaseID.
> .  NUMERIC X1 X2  (F5.2).
> .  LOOP    CaseID = 1 TO 125.
> .     COMPUTE #Common = RV.NORMAL(0.1*CaseID,3).
> .     COMPUTE #Delta  = RV.NORMAL(0.71,1).
> .     COMPUTE X1      = #Common - #Delta/2.
> .     COMPUTE X2      = #Common + #Delta/2.
> .     END CASE.
> .  END LOOP.
> .  END FILE.
> END INPUT PROGRAM.
>
> T-TEST
>    PAIRS = X1  WITH X2 (PAIRED)
>    /CRITERIA = CI(.95)
>    /MISSING = ANALYSIS.
>
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> command. To leave the list, send the command
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Professor Diana Kornbrot
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