Understanding data & statistical terminology You can have data - - PowerPoint PPT Presentation

Understanding data & statistical terminology

“You can have data without information, but you cannot have information without data.”

Daniel Keys Moran (Computer programmer and science fiction author)

Trembling aspen

(Populus tremuloides)

Western North America distribution

Aspen frequency

% Forest Cover

Central location of aspen population

n=100 samples take at each

Trembling aspen

(Populus tremuloides)

Western North America distribution

Central location of aspen population

n=100 samples take at each

Can the data we collect in AB realistically be used to make inferences about Aspen in Colorado? So what is our population?

Aspen frequency

% Forest Cover

Trembling aspen

(Populus tremuloides)

Western North America distribution

Central location of aspen population

n=100 samples take at each

What if all the samples came from northern mixedwood ecosystems north of High Level, AB? What can we realistically make inferences about?

High Level

Aspen frequency

% Forest Cover

Example 1: Lentil dataset (Your new best friend)

Farm 1 Farm 2

Plot

1 Variety in each

Individual lentil plants

A A A A A A A B B B B B A B C C C C C C C C Do yield of different lentil varieties differ at 2 farms? Do the varieties differ among themselves?

Golden rules for data tables

• 1. A row represents a unit

– All measurements of a unit should normally be in the same row. – Different units must be in different rows. – Important to think about what your units are

Golden rules for data tables

• 2. If in doubt, add more rows

– If possible, use categorical (character) variables to indicate the independent effects (treatments, environments). – Repeat measurement (e.g. time series data) normally get individual rows (e.g. time is added as a column) – It is always easy to convert a long table to a wide table (Excel Pivot), but not vice versa.

Example 2: Animal tracks

Forest stand Transect Animal tracks

Is there a difference in the use of forest corridors in different stand types by ungulates?

Conifer dominated Deciduous dominated

Other useful statistical terms

• Experiment – any controlled process of study which results in data collection, and which the
• utcome is unknown
• Descriptive statistics – numerical/graphical summary of data
• Inferential statistics – predict or control the values of variables (make conclusions with)
• Statistical inference – to makes use of information from a sample to draw conclusions

(inferences) about the population from which the sample was taken

• Parameter – an unknown value (needs to be estimated) used to represent a population

characteristic (e.g. population mean)

• Statistic – estimation of parameter (e.g. mean of a sample)
• Sampling distribution (aka. Probability distribution or Probability density function) – probability

associated with each possible value of a variable

• Error - difference between an observed value (or calculated) value and its true (or expected)

value