An experiment was conducted to evaluate the effect of seeding clouds on rainfall

Question

An experiment was conducted to evaluate the effect of seeding clouds on rainfall with silver nitrate. 26 of 52 clouds were randomly selected to receive the seeding, the other 26 had no seeding (a control). The resulting data are provided below. Assume equal variances and conduct a statistical comparison of the mean rainfall. What conclusions do you draw? Conduct a test for equality of variances between the seeded and unseeded data. What conclusions do you draw? Assume unequal variances and conduct a statistical comparison of the mean rainfall. What conclusions to you draw?

Explanation / Answer

a) Assuming equal variance:

H0: Means of two groups are same

H1: Atleast one group is same.

Alpha: 5% Level

Test statistic:

From Excel

Conclusion: t cal=3.3254

t critical value=2.063

t cal > t critical value we reject the Ho

C)

H0: Means of two groups are same

H1: Atleast one group is same.

Alpha: 5% Level

Test statistic:

From Excel

When unequal variances

t-Test: Two-Sample Assuming Unequal Variances

Conclusion: t cal=3.3254

t critical value=2.16037

t cal > t critical value we reject the Ho

t-Test: Two-Sample Assuming Equal Variances seeded unseeded Mean 85.30769231 21.15384615 Variance 4683.730769 154.6410256 Observations 13 13 Pooled Variance 2419.185897 Hypothesized Mean Difference 0 df 24 t Stat 3.325406609 P(T<=t) one-tail 0.001415331 t Critical one-tail 1.71088208 P(T<=t) two-tail 0.002830662 t Critical two-tail 2.063898562

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