Effect Size

[lph2005]

I am not sure how to use effect size within SPSS because Cohen's d is not part of SPSS. I'm trying to use G*Power - and getting the values from SPSS.

ANOVA returned significance value greater than .05. Instead of leaving the analysis as I cannot reject the null, I wanted to verify power. I understand that power is calculated from the sample size, alpha, and ES. I have G*Power but really do not understand the correct options.

sample size = 145
alpha = .05 (or do I use .804?)
eta squared was calculated from ANOVA table = .003 [update: using G*Power, effect size f was calculated from the means and sample size to be .31]

This is what is written so far .. without statement of power.
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A one-way between groups analysis of variance (ANOVA) was conducted to explore the impact of job assignment on the level of intent to stay. Assumptions of the test include one independent grouping variable (job assignment) and one dependent continuous variable (intent to stay index). Results are shown in Table 11. The test revealed no statistically significant difference in intent to stay across three job assignment groups; the significance value of .804 suggested there was no statistically significant difference at the p < .05 level. No further analyses were performed on this data and the null hypothesis (H60) was not rejected because of the small p-value. This does not mean differences do not exist; only the data collected do not support the rejection of the null hypothesis.
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The effect size statement is not included because I am not sure how to interpret a .003 (very small). Does that mean the no statistical difference is because the sample size to see a difference is too small?

Hopefully this is enough information for someone to help. Thank you !