Statistics

homework_-_week_2.pdf

AGSC 5060 – Statistics for Research Homework

Page – 1 of 2

Homework – Week 2 (due Feb 3, 2015 before the class. Please print hard copy of the homework and

bring it with you to the class. We will mark it by using iclicker at the beginning of the class)

Descriptive Statistics

Researchers employ wide range of statistical methods to analyze the data they have collected from

experiments and observational studies. Summarizing, describing and interpreting the raw data are the

initial steps towards developing a story. It generally uses descriptive statistics such as means, standard

deviations, percentiles, minimum, maximum, number of samples (n) and graphical methods to

understand the data. In this homework, you will use Microsoft Excel to summarize large array of data,

which enables us to tabulate various summary statistics and generate histogram. Such visual and

numerical characterization of the data forms the basis to make any inferences.

Microsoft Excel is very useful when summarizing data using its Pivot Table functionality. In this

homework you will be using pivot table to summarize tree diameter at the breast height (dbh) data by

species and ecosites. Such functionality in excel is flexible to summarize data by classes or categories.

Download tree.xls data along with its metadata file from elearn. Visually inspect the data and review

variables, their scale of measurement and number of cases (number of observations) in the dataset.

In Excel, select all the data (Ctrl+A) and choose the ribbon “Insert” > click “Pivot Table”. In the new

dialogue box, select a table or range of data you want to analyze (tree!A$1:E$24471) radio button and

also choose new worksheet radio button; then click OK.

a) calculate means, standard deviations, maximum value, minimum value and number of samples

for

i. all dataset,

ii. by species,

iii. by ecosites, and

iv. All combinations of ecosites and species

b) Plot a histogram showing the distribution of the dbh ( , where Max is

maximum dbh and Min is minimum dbh and n is number of samples). Round the bin width to

nearest one decimal place number. Then generate class size by using the bin width and

minimum dbh in the dataset.

Note: your table (for question a) should look like table 1 in page 2.

AGSC 5060 – Statistics for Research Homework

Page – 2 of 2

Table 1. Summary statistics of the tree diameter at the breast height (dbh) for nine boreal tree species

and two ecosite groups in boreal forests of Northern Ontario, Canada. Data were collected during June

–July, 2012.

Ecosites/Species dbh (cm)

mean Std Dev Min Max n

B049

B127

Total

Figure 1. Diameter distribution for boreal tree species in Ontario, Canada. Data were collected

during June –July, 2012.