CF Data Analysis & Reporting 2 — Questions and Answers
Question 1: A forester measures DBH for 50 trees and gets a mean of 18 cm with a standard deviation of 4 cm. What is the coefficient of variation (CV)?
- 12.5%
- 22.2% (Correct answer)
- 8.0%
- 18.4%
Correct answer: 22.2%
CV = (standard deviation / mean) × 100 = (4/18) × 100 = 22.2%.
Question 2: Which sampling design is most appropriate when a forest stand has clearly distinct zones of high-density and low-density trees?
- Simple random sampling
- Systematic sampling
- Stratified random sampling (Correct answer)
- Cluster sampling
Correct answer: Stratified random sampling
Stratified random sampling divides the population into homogeneous strata, improving precision when distinct zones exist.
Question 3: In a forest inventory report, the term 'basal area per hectare' is expressed in which units?
- cm²/ha
- m²/ha (Correct answer)
- m³/ha
- trees/ha
Correct answer: m²/ha
Basal area per hectare is expressed in m²/ha, representing the cross-sectional area of tree stems at breast height per unit area.
Question 4: A forester uses a relascope with a basal area factor (BAF) of 10. She tallies 14 'in' trees at one point. What is the estimated basal area per hectare?
- 100 m²/ha
- 140 m²/ha (Correct answer)
- 14 m²/ha
- 1.4 m²/ha
Correct answer: 140 m²/ha
Estimated basal area = number of 'in' trees × BAF = 14 × 10 = 140 m²/ha.
Question 5: Which statistical test is used to compare the means of two independent groups of tree height measurements to determine if they differ significantly?
- Chi-square test
- Paired t-test
- Independent samples t-test (Correct answer)
- ANOVA
Correct answer: Independent samples t-test
An independent samples t-test compares means from two unrelated groups to test for statistically significant differences.
Question 6: What does the 'p-value' in a statistical test represent?
- The probability that the null hypothesis is true
- The probability of observing results at least as extreme as those found, given the null hypothesis is true (Correct answer)
- The proportion of variance explained by the model
- The effect size of the treatment
Correct answer: The probability of observing results at least as extreme as those found, given the null hypothesis is true
The p-value is the probability of obtaining a result as extreme as the observed one if the null hypothesis were true.
Question 7: In forest inventory data, a positively skewed distribution of tree volumes would indicate that:
- Most trees are very large with a few small ones
- Most trees are small or average-sized with a few very large outliers (Correct answer)
- The data follows a normal distribution
- Tree volumes are uniformly distributed
Correct answer: Most trees are small or average-sized with a few very large outliers
Positive skew means the tail extends to the right, indicating most observations are lower with a few very high values.
CF Data Analysis & Reporting 2
A forester measures DBH for 50 trees and gets a mean of 18 cm with a standard deviation of 4 cm.
What is the coefficient of variation (CV)?