Please interpret the output below. What type of test was used and why? Are energy costs lower for LEEDcertified buildings in this output? These data have an effect size of d = .39. How does that add to your interpretation of the results?
Yearly Energy Costs LEED Certified Buildings (in thousands of $) 
Yearly Energy Costs nonLEED Certified Buildings (in thousands of $) 

Mean 
18.22 
21.46 

Variance 
1548.27 
1318.33 

Observations 
60 
55 

Hypothesized Mean Difference 
0 

df 
73 

t Stat 
1.678 

P(T<=t) onetail 
0.048 

t Critical onetail 
1.667 

P(T<=t) twotail 
0.096 

t Critical twotail 
1.993 
Here student independent sample 't' test was used.
Reason: Here two independent groups are there and also we are testing mean energy costs between two groups.
IT IS A ONE  TAILED TEST
Here research hypothesis is Are energy costs lower for LEEDcertified buildings in this output?
Ho: mean difference = 0 Vs. H1: mean1<mean2
Therefore tstatistic = 1.678 and one tailed p = 0.048
Here p <0.05 hence we reject Null hypothesis.
Conclusion: There was an enough evidence that the energy costs lower for LEEDcertified buildings
Here effect size of d = .39, it indicates medium effect i.e. likely to be different in the means.
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