CO2 Uptake Experiment
This example is taken from an experiment listed in the R help files under ?CO2.
“An experiment on the cold tolerance of the grass species Echinochloa crus-galli was conducted. The CO2 uptake of six plants from Quebec and six plants from Mississippi was measured at several levels of ambient CO2 concentration. Half the plants of each type were chilled overnight before the experiment was conducted.” Plants were considered tolerant to the cold if they were still able to achieve high CO2 uptake values after being chilled.
Ignoring the Plant ID for a moment, there are three factors that possibly effect the uptake of a plant. These include Type, Treatment, and conc. The factor Type has two levels, Quebec and Mississippi. The factor Treatment has two levels chilled and nonchilled and the factor conc has seven levels 95, 175, 250, 350, 500, 675, and 1000.
Conc is related to the ambient concentration of CO2.
Our main interest is CO2 uptake and how the other factors impact it. We will first do a univariate analysis of uptake.
Create a table with the overall summary statistics for uptake:
# This is NEW! if you tell R to knit the favstats output using the "kable" function, it will look a lot nicer when the document is rendered.
knitr::kable(favstats(CO2$uptake))| min | Q1 | median | Q3 | max | mean | sd | n | missing | |
|---|---|---|---|---|---|---|---|---|---|
| 7.7 | 17.9 | 28.3 | 37.125 | 45.5 | 27.2131 | 10.81441 | 84 | 0 |
Create a histogram of the CO2 uptake across all groups:
We will now look at how other factors might impact CO2 uptake.
Create a table of summary statistics of uptake for each Type of plants used in the experiment.
Create a side-by-side boxplot of uptake for each Type of plants used in the experiment.
Create a table of summary statistics of uptake for each Treatment used in the experiment.
Create a side-by-side boxplot of uptake for each Treatment used in the experiment.
Create a table of summary statistics of uptake for each level of ambient CO2, conc, found in the experiment.
Create a side-by-side boxplot of uptake for each level of ambient CO2, conc, found used in the experiment.
The background suggests this study was an experiment. In your own words, describe the difference between an experiment and an observational study.
What might this study have looked like if it had been an observational study?
Describe in your own words what the population of this study could be. How broad can we make our conclusions?
If you were to recommend a planting scenario to maximize CO2 uptake, what would you recommend based on the summaries provided?