(urgent) Sample Size

Frequently asked questions about PLS path modeling.
misterhussein
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(urgent) Sample Size

Post by misterhussein »

Hi All,

Please advise me how to determine the appropriate sample size for running 2x2 factorial design by using PLS.

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allenjia
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Post by allenjia »

above 1000, 5000 is recommended by Dr. Chingle
Do the formative by using PLS!!
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Diogenes
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Post by Diogenes »

Hi,

1000 or 5000 is recommended to the bootstrap procedure.

To the 2x2 factorial design I thought:

1) ANOVA to compare 4 groups (mean) = 180 cases [alpha = 5%, power = 80%, effect size = medium = 0.25]

2) Multigroup comparison (two independent path coefficients) = 356 cases [alpha = 5%, power = 80%, effect size = medium = 0.3]

See (Cohen, 1977) and use G*Power 3 (Faul, Erdfelder, Lang, & Buchner, 2007), it is free.


Cohen, J. (1977). Statistical power analysis for the behavioral sciences (Revised.). New York: Academic Press.
Faul, F., Erdfelder, E., Lang, A.-G., & Buchner, A. (2007). G*Power 3: a flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behavior research methods, 39(2), 175-91.


Best regards,

Bido
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Post by anugrah »

Hi All,

I hv the same problem too..
Please advise me how to determine the appropriate sample size for running 91 observations by using PLS?
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Post by husseins »

Halo Pak Anugrah,

Maybe you can try this:

Chin (1998) the sample required for PLS can be determined in the following ways: 1) the construct with the largest number of formative indicators or 2) the dependent latent variable with the largest number of relationship. The sample size required would be 5 to 10 times of either 1) or 2) whichever is higher

Semoga membantu...

Salam,
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Diogenes
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Post by Diogenes »

Hi

The best way is using power analysis:
1) How many arrows arrive in each LV?
2) Choose the biggest number
3) Use this number as number of predictors in the multiple regression procedure in the G*Power to have the sample size.

Software G*Power 3 available at
http://www.psycho.uni-duesseldorf.de/ab ... p/gpower3/

Best regards,
Bido
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Post by anugrah »

Thank you for reply my question Pak Hussein and Mr Bido,

I owned a maximum of 7 LVs, will that mean my sample size is 70?
Can a sample size be smaller that the total number of cases?
(cases=91)

If i use G*Power3, i find 2 types.
There are 2 linear multiple regression
1) Fixed model, R2 deviation from zero (I have 138 sample sizes)
2) Fixed model, R2 increase (I have 107 sample sizes)

Which one should i use?
Is that ok from that results? or should be above 1000?

NB:
My model is hierarchical component model (repeated indicator approach)
Image

Kind Regard
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Diogenes
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Post by Diogenes »

f2 = .15 --> R2 = 13% medium
alfa = 5%
Power = 80%
Predictors = 2 (KPR & KPS) = maximum number of the arrows arriving in a LV.
Sample size = 68 cases

Best regardss,

Bido
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Post by anugrah »

Test> Correlation and regression>multiple regression:fixed model, R2 deviation from zero.(is it true?)

Why should i use 80% not 95%? [80% = 68 samples; 95% = 107 samples]
and where can i find/calculate R2 from G*Power?
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Diogenes
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Post by Diogenes »

Hi,

1) Yes.

2) 0.8 is the minimum value recommended by Hair Jr. et al., but it depends of the field of research, in fact the default value of the G*Power is .95.

3) G*Power gives us the effect size (f2), and we need to compute the R2, see:

FAUL, F.; ERDFELDER, E.; LANG, A.-G.; BUCHNER, A. G*Power 3: a flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behavior research methods, v. 39, n. 2, p. 175-91, 2007.

f2 = R2/(1 – R2) [Faul et al., 2007, p.181]

R2 = f2/(1 + f2)


Best regards,

Bido
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Post by mazi »

i have 8 construct. for loyalty construct there are 4 direct predictor, s for using the mentioned software.
i can go to the
test> correlation and regression> linear multiple R2 zero
and for estimating the sample size
how i can acquire the effect size?
as you said
power=0.8
alpha=0.05
number of predictor is 4
but what about effect size?[/img][/list]
mazi
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value of f2 in Gpower

Post by mazi »

is it true for my sample size 85? i dont know which vaue insert in effect size box?. for powe i insert 0.8. for alpha 0.05, and because 4 paths arrived ate loyalty which is the maximum i set 4 for number of predictor
but i dont know about number of f2? coul you please help me calculate sample size with Gpower?
Thank you
Nazila Babakhani
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Diogenes
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Post by Diogenes »

Hi,

the classification given by Cohen and used in G*Power are:
.02 = small
.15 = medium
.35 = large

With .02 the sample will be able to detect small effects as significant.

With .36 the sample will be able to detect just large effects (R2 greater than .26) as significant.

Best regards,

Bido
mazi
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Post by mazi »

so you mean that small effect size give more sample size which is better? which of them should i use?
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Nazila Babakhani
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Diogenes
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Post by Diogenes »

With “small effects” your sample will be larger, and more sensible, it will detect small effects as significant.

Usually, to collect data is a problem (cost, time..) and we use the “medium effect”.

Remembering that with small samples we could finish with a model where nothing is significant.

Best regards,

Bido
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