Collecting Data

In the sciences we collect data by sampling individuals from a population, then using that sample to

Population > Sample > Individual

infer about the population as a whole. The picture to the right (from: correctly illustrates the process, but note that many websites are mistaken about this.

The ideal way to sample a population so that your data are statistically valid is to take a random sample, where every individual in the original population has an equal probability of being sampled. The best way to take a proper random sample is to number every individual in the population then to use a random number table to pick which individuals to sample. In practice that is usually impossible so we often use other methods to take a random sample, as follows:

  • select every nth individual encountered, where n is determined from a random number generator (or table)
  • randomly select locations to sample within the population distribution
  • divide the population into equal groups or equal ranges and select random individuals within each section, either by random locations or some other sampling method

Many other kinds of samples are sometimes (often?) called random, but they are not and should be referred to correctly:

  • haphazard sample: you just guess which individuals to include in your sample—this method is often called random but it’s not
  • convenience sample: you sample the individuals that are readily available to you

To get some random numbers for your sampling, go to where you can generate a random sequence of numbers between any two numbers. Note that this method ensures that each number is listed only once. Another random number generator at that site (here) samples with replacement such that you might get the same number more than once. That whole site (here) is an excellent source of information about random numbers and random number generators

I've spent more time than many will believe [making microscopic observations], but I've done them with joy, and I've taken no notice those who have said why take so much trouble and what good is it?

Antonie van Leeuwenhoek

It's a parts list... If I gave you the parts list for the Boeing 777 and it had 100,000 parts, I don't think you could screw it together and you certainly wouldn't understand why it flew

Eric Lander

What is true for E. coli is also true for the elephant

Jacques Monod

The world becomes full of organisms that have what it takes to become ancestors. That, in a sentence, is Darwinism

Richard Dawkins

Shall we conjecture that one and the same kind of living filaments is and has been the cause of all organic life?

Erasmus Darwin

Nature proceeds little by little from things lifeless to animal life in such a way that it's impossible to determine the line of demarcation


Cells let us walk, talk, think, make love, and realize the bath water is cold

Lorraine Lee Cudmore

In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Light will be thrown on the origin of man and his history

Charles Darwin

It is my belief that the basic knowledge that we're providing to the world will have a profound impact on the human condition and the treatments for disease and our view of our place on the biological continuum

J. Craig Venter

Imagine a house coming together spontaneously from all the information contained in the bricks: that is how animal bodies are made

Neil Shubin

A grain in the balance will determine which individual shall live and which shall die - which variety or species shall increase in number, and which shall decrease, or finally become extinct

Charles Darwin

The stuff of life turned out to be not a quivering, glowing, wondrous gel but a contraption of tiny jigs, springs, hinges, rods, sheets, magnets, zippers, and trapdoors, assembled by a data tape whose information is copied, downloaded and scanned

Steven Pinker

We wish to discuss a structure for the salt of deoxyribose nucleic acid. (D.N.A.). This structure has novel features which are of considerable biologic interest

Rosalind Franklin

We are biology. We are reminded of this at the beginning and the end, at birth and at death. In between we do what we can to forget

Mary Roach

The systems approach to biology will be the dominant theme in medicine

Leroy Hood

I've always been interested in animal behavior, and I keep reading about it because it's so surprising all the time - so many things are happening around us that we neglect to look at. Part of the passion I have for biology is based on this wonderment"

Isabella Rossellini

Because all of biology is connected, one can often make a breakthrough with an organism that exaggerates a particular phenomenon, and later explore the generality

Thomas Cech

Nothing in Biology makes sense except in the light of evolution

Theodosius Dobzhansky

Biology is now bigger than physics, as measured by the size of budgets, by the size of the workforce, or by the output of major discoveries; and biology is likely to remain the biggest part of science through the twenty-first century

- Freeman Dyson

Nothing can be more incorrect than the assumption one sometimes meets with, that physics has one method, chemistry another, and biology a third

- Thomas Huxley