Question

Agriculture near Lake Okeechobee focuses heavily on sugar cane fields and citrus groves. These crops require supplemental fertilizer, such as nitrates and phosphates, to be added to the soil. Many farms apply a set amount of fertilizer. Any leftover fertilizer that was not absorbed into the soil or used by the plants is washed away by rainwater into streams that flow from Lake Okeechobee to the Everglades. Some farms are testing variable fertilization, which involves testing the soil and then adding only the required amount of fertilizer. You have been provided with data on nitrate levels (ug/L) in streams near farms from two years: 2014 (when the farms were using a set amount of fertilizer) and 2017 (after the farm switched to the variable fertilizer method). For both years, sampling was conducted by collecting water samples from 35 streams near these farms. Based on observations of water in streams near these farms during 2014 and 2017, we could ask the following question: Has the nitrate level (ug/L) in streams near farms changed with the adoption of variable fertilization methods?

1. For the study above, identify the following: (4 points)

a. Population: The average nitrate levels on all the streams near farms.

b. Sample: The average nitrate levels on 35 streams that were sampled.

c. Parameter:

d. Statistics:

2. For the study above, identify the following: (3 points)

a. Dependent Variable

b. Independent Variable

c. Is the independent variable categorical or numerical?

3. Write a null, two-tailed alternative, and one-tailed alternative statistical hypothesis for this study. (3 Points)

Answer 1

1. For the study above, identify the following: (4 points)

a. Population: All the streams that flow from Lake Okeechobee to the Everglades.

b. Sample: The sample is 35 streams near the farms that flow from Lake Okeechobee to the Everglades.

c. Parameter: The population average nitrate levels on all the streams near farms.

d. Statistics: The sample mean nitrate levels in 35 streams near the farms.

2. For the study above, identify the following: (3 points)

a. Dependent Variable - The nitrate level (ug/L) in streams near farms

b. Independent Variable - Fertilization methods - (set amount of fertilizer or variable fertilizer method)

c. Is the independent variable categorical or numerical? - The independent variable is a categorical variable with 2 levels.

3. Write a null, two-tailed alternative, and one-tailed alternative statistical hypothesis for this study.

Null Hypothesis H0: Average nitrate levels in streams near farms are equal for set amount of fertilizer and variable fertilizer method.

Two-tailed alternative Ha: Average nitrate levels in streams near farms for set amount of fertilizer is not equal to the average nitrate levels in streams near farms for variable fertilizer method.

One-tailed alternative Ha: Average nitrate levels in streams near farms for set amount of fertilizer is greater than the average nitrate levels in streams near farms for variable fertilizer method.