Cloud seeding is used to increase precipitation by dispersing substances (silver

Question

Cloud seeding is used to increase precipitation by dispersing substances (silver iodide, dry ice, table salt) Into the air that serve as cloud condensation. Simpson (1975, Technometrics) reported the results on 26 seeded and 26 unseeded clouds in order of the amount of rainfall (In acre-feet), largest amount first. Here are 2 possible tests to study the question of whether cloud seeding work: Ch 6.3.2 Paired t-Test of mu(Seeded - Unseeded) T-Test of H_0: mu(Seeded - Unseeded) = 0 against H_A: mu(Seeded - Unseeded) > 0 t-Statistics = 3.64 with 25 df P-Value = 0.0006 Ch 6.3.3 2-SampZTest of mu(Seeded) - mu(Unseeded) H_0: mu(Seeded) - mu(Unseeded)= 0 against H_A: mu(Seeded) - mu(Unseeded) > 0 z-Statistics = 1.9953 x_secded - x_unseeded =277.1 P-Value = 0.0230 a. Which of these 2 tests is appropriate for these data? Explain. b. Using the test you selected in part (a) and alpha = 0.01, state your conclusion in context of the problem.

Explanation / Answer

ANSWER:

a) 2-Sample 'z' test is appropriate for comprison of two means

EXPLANATION: Here there are two groups, and we are testing the mean difference between seeded and unseeded clouds. Therefore 'z' test for difference of means appropriate for comparison.

Paired 't' test is not suitable. It is suitable for paired data. Paired data means each individual gives pair of observations.

b) Here p = 0.023 > 0.01

Hence we accept Ho. (both the means are equal)

i.e. there was no significant evidence to the accepting the alternative hypothesis.

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