The boxplots to the right summarize the heights in centimete

The boxplots to the right summarize the heights, in centimeters, of approximately 400 pine seedlings six years after they were planted at a center for environmental study. Approximately half of the trees were fertilized yearly, and the remaining trees were never fertilized. a) Was this an experiment, observational study, or sample survey? Explain. b) Interpret the third quartile for the unfertilized trees in context.

Solution

First of all let us try to understand the diffeence between an experiment, an observational study and a survey .

In an experiment investigators apply treatments to experimental units (people, animals, plots of land, etc.) and then

proceed to observe the effect of the treatments on the experimental units .i.e, The entire sample is influenced by

the experimenters.

In an observational study the investigators observe subjects and measure variables of interest without assigning treatments to the subjects. The treatment that each subject receives is determined beyond the control of the investigator .The investigator simply observes the results and measures it.

Surveys are one form of an observational study, since the investigators do not influence the outcomes. Statistical surveys collect information from a sample group to learn about the entire population. A survey may focus on opinions or factual information depending upon the purpose of the study.

Now let us focus on our problem at hand. Let us observe as to what is happening ?

In this case, the investigators, are

1. measuring the height of pine seedlings after six years in two catagories(fertilized and unfertilized)

2. The investigators are providing fertilizers to half of the pine seedlings . They are influencing the sample in question.

3. We do not have any information if the result that is acheived is as per a part of any survey questionaire or not.

Since the investingators are trying to simulate two diffferent condictions for the seedlinds by providing fertilizers ,we can say that the sample in question is an experiment.

b. We can interpret that the third quartlie of sample data set of unfertilized seedlings is

1. Approximately 170 centimeters.

2. Lesser then 3rd quartile of sample data of fertilized sample.

3. Approximately 150 unfertilized seedlings attained height of approximately 170 cms.

4. For unfertilized seedlings sample set, there is a huge difference between the average height and height attained

by 75% of its sample (170-125 cm =45 cm)