In: Statistics and Probability
This dataset contains two variables: fertilizer type (1, 2, or 3) and crop yield per square foot. Using ANOVA, test the null hypothesis that the three fertilizers are equally effective. Hint: Notice that the data are arranged in what's called a "long" format (one long column of data). To you ANOVA, you first need to rearrange the data into three columns.
1. What is the value of the F-statistic? Answer
2. What is the p-value that the three means are the same?
Answer
3. At α=.05, should the null hypothesis be rejected?
AnswerRejectDon’t reject
4. Which fertilizer should you choose based on these results (be careful here!)?
Data Set
fertilizer | yield |
1 | 177.228692 |
1 | 177.550041 |
1 | 176.408462 |
1 | 177.703625 |
1 | 177.125486 |
1 | 176.778342 |
1 | 176.746302 |
1 | 177.061164 |
1 | 176.274949 |
1 | 177.967203 |
1 | 176.6013 |
1 | 177.030543 |
1 | 177.479507 |
1 | 176.87413 |
1 | 176.114388 |
1 | 176.008395 |
1 | 176.108313 |
1 | 178.357441 |
1 | 177.262445 |
1 | 176.918845 |
1 | 176.239016 |
1 | 176.57307 |
1 | 176.039298 |
1 | 176.817922 |
1 | 176.160587 |
1 | 177.226424 |
1 | 175.938533 |
1 | 177.164937 |
1 | 175.36084 |
1 | 177.276996 |
1 | 175.945444 |
1 | 175.88278 |
2 | 176.479341 |
2 | 176.044342 |
2 | 177.412462 |
2 | 177.360818 |
2 | 177.385499 |
2 | 176.975808 |
2 | 177.379779 |
2 | 177.997995 |
2 | 176.434863 |
2 | 176.933265 |
2 | 175.98348 |
2 | 177.034093 |
2 | 176.436762 |
2 | 176.067745 |
2 | 177.121049 |
2 | 177.197721 |
2 | 176.603724 |
2 | 177.208171 |
2 | 177.148829 |
2 | 176.819077 |
2 | 176.999067 |
2 | 178.134605 |
2 | 176.429156 |
2 | 176.668323 |
3 | 177.104186 |
3 | 178.079635 |
3 | 176.903422 |
3 | 177.540284 |
3 | 177.03271 |
3 | 178.286042 |
3 | 176.40541 |
3 | 176.43083 |
3 | 177.396331 |
3 | 176.925576 |
3 | 177.055046 |
3 | 177.344164 |
3 | 177.128368 |
3 | 177.168302 |
3 | 176.353941 |
3 | 179.060899 |
3 | 176.300517 |
3 | 177.593352 |
3 | 177.115245 |
3 | 177.794457 |
Solution:
We can use the excel "ANOVA:Single Factor" data analysis tool to find the answer to the given questions. The excel output is given below:
Anova: Single Factor | ||||||
SUMMARY | ||||||
Groups | Count | Sum | Average | Variance | ||
1 | 32 | 5656.22542 | 176.7570444 | 0.469119716 | ||
2 | 24 | 4246.255974 | 176.9273323 | 0.31409632 | ||
3 | 20 | 3545.018717 | 177.2509359 | 0.475272296 | ||
ANOVA | ||||||
Source of Variation | SS | df | MS | F | P-value | F crit |
Between Groups | 3.008554181 | 2 | 1.50427709 | 3.565667772 | 0.033304083 | 3.122102932 |
Within Groups | 30.79710019 | 73 | 0.421878085 | |||
Total | 33.80565437 | 75 |
1. What is the value of the F-statistic?
Answer: F = 3.566
2. What is the p-value that the three means are the same?
Answer: p-value = 0.0333
3. At α=.05, should the null hypothesis be rejected?
Answer: Reject
4. Which fertilizer should you choose based on these results (be careful here!)?
Answer: We should choose the fertilizer type 2