MR317 Introduction to Marine Ecology - Biostatistics

LecturesMartin Ryan Seminar RoomMonday 11am, Tuesday 9amTuesday 12 pm, Friday 9 am

MINITAB PracticalsRoom 201 Arts Millenium Building

starting 16/01/06 Monday 2 – 5 pm

Emma HolianRoom 108, Riverside Terrapin

Email: emma.holian@nuigalway.ie

Dr. Jochen EinbeckRoom 209, Áras de Brún

Email: jochen.einbeck@nuigalway.ie

Lecturers:

Lecture Material

• Handouts, notes• Web based material

http://www.nuigalway.ie/maths/je/marine– Notes, these slides– Datasets

Course Content• Basic ideas – revision• Looking at data – summaries, plots, etc• Statistical analyses

– Comparing groups– Regression– Analysis of variance – Simple multivariate methods

• Aspects of study design• Use of MINITAB package

Population : the entire group of objects about which information is required.

Collecting Data

A parameter is a numerical characteristic of the population.

It is a fixed number, but we usually do not know its value.

Unit: any individual member of the population

Sample: a part or subset of the population used to gain information about the population.

Sampling Frame: the list of units from which the sample is chosen.

Geographical/Spatial coordinates.

Variable: a characteristic of a unit to be measured in the sample.

Data are the values that variables can assume.

Variable

Qualitative Quantitative

Discrete Continuous

Nominal Ordinal

The value of the statistic changes from sample to

sample.

Statistics ARE numbers derived from a sample

of data.

Example 1

Population: Irish Sea

Unit ?

Sample ?

Variable ?

Sampling Frame ?

PopulationParameters

Inference

SampleStatistics

Sample

Inference is the process of making decisions about a

population based on information contained in a

sample from that population.

• Descriptive statisticsconsists of the collection, organisation, summarisation, and presentation of data.

• Inferential statisticsconsists of generalisingfrom samples to populations, performing hypothesis testing, determining relationships among variables, and making predictions.

General philosophy

How do we select a small subset of a population

representative of the whole population?

Using your best judgement, take a representative sample

of 6 circles from the population of 60 circles and use the sample mean as an

estimate of the true population mean

1

1.5

2 3

2.5

0.5N=60

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

0

50

100

150

200

250

Judgement

Freq

uenc

yJudgement Sample

0.5 1.0 1.5

0

50

100

150

SRS

Freq

uenc

ySimple Random Sample

0.5 1.5 2.5

0

50

100

150

Judgement and SRS

Freq

uenc

y

One consequence of natural variation is that two samples drawn by the same method from the same

population will give somewhat different estimates of the population parameters (sampling variation).

Understanding variation

Statistics deals with discriminating between variation that is scientifically interesting and

variation that just reflects background variation.