Missing Normality - What to do? Solution please!

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Chidambaram
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Joined: Tue Apr 05, 2011 10:29 am

Missing Normality - What to do? Solution please!

Postby Chidambaram » Thu Nov 15, 2012 10:45 am

My research involves a sample size of 794 about personality and bias. While ensuring the data normality thru SPSS and it's giving the following: (It is only an excerpt)

Tests of Normality
Kolmogorov-Smirnovaa Shapiro-Wilk
Statistic df Sig. Statistic df Sig.
Q1 .154 794 .000 .911 794 .000
Q2 .238 794 .000 .880 794 .000
Q3 .249 794 .000 .882 794 .000
Q4 .168 794 .000 .911 794 .000
Q5 .165 794 .000 .914 794 .000
a. Lilliefors Significance Correction

The above sig values are not supporting the normality of data, as it is less than 0.05. (For all 50 questions - sig value is .000). BUT

www.psychwiki.com/images/7/79/Lab1DataScreening.doc - advises in page 9 that - “Test of Normality” box gives the K-S and S-W test results. If the test is NOT significant, then the data are normal, so any value above .05 indicates normality. If the test is significant (less than .05), then the data are non-normal. In this case, both tests indicate the data are non-normal. However, one limitation of the normality tests is that the larger the sample size, the more likely to get significant results. Thus, you may get significant results with only slight deviations from normality. In this case, our sample size is large (n=327) so the significance of the K-S and S-W tests may only indicate slight deviations from normality. You need to eyeball your data (using histograms) to determine for yourself if the data rise to the level of non-normal.


Now i am confused about my future course of action!

Can i go ahead with the same set of data for parametric tests?

Looking forward for help desperately!

Regards
Chidams
statman
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Re: Missing Normality - What to do? Solution please!

Postby statman » Thu Nov 15, 2012 1:37 pm

Exactly what are you trying to find out and some more about the data - See the Note below
See the note below

NOTE: Please read the Posting Guidelines and always tell us your OS, the SPSS version and information about your study and data!

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Chidambaram
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Re: Missing Normality - What to do? Solution please!

Postby Chidambaram » Fri Nov 16, 2012 12:01 pm

Sorry for missing those info!

My system's OS is Windows Vista Premium Home Edition.

SPSS: 16

Research area: Finance - Link between Personality and Bias.

N. Chidambaram
statman
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Re: Missing Normality - What to do? Solution please!

Postby statman » Fri Nov 16, 2012 1:40 pm

So you are looking to see if there is a cause/affect relationship between Finance (DV) and IVs Personality and Bias?

Describe the data types, e.g., is Finance scale, ordinal, ....
Chidambaram
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Re: Missing Normality - What to do? Solution please!

Postby Chidambaram » Sat Nov 17, 2012 12:34 pm

Yes. Absolutely. eg.

scales are: Very Inaccurate Moderately Inaccurate Neither Inaccurate Nor Accurate Moderately Accurate Very Accurate ( in the order of 1 to 5 )


1. … I am the life of the party. 1 2 3 4 5
2. … I feel little concern for others. 1 2 3 4 5
3. … I am always prepared. 1 2 3 4 5
4. … I get stressed out easily. 1 2 3 4 5
5. … I have a rich vocabulary. 1 2 3 4 5


Further in terms of Bias: (eg)

1. I am an excellent trader/investor. scales are Strongly Disagree Disagree Neutral Agree Strongly Agree

Now just i attempted to ensure the personality related questions normality only.
statman
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Re: Missing Normality - What to do? Solution please!

Postby statman » Sat Nov 17, 2012 12:48 pm

Look into the set of P-P charts and the Help associated with them. Sometimes they are better than pure stats

Also, review the data considerations for Categorical Regression

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