1. Estimations & Random Samples
COUNTING POPULATIONS
Estimations & Random Samples

2. What are the 3 biggest populations in this pond community?
Name of Population
Ducks
Cattails
Water Lilies
Actual Count
Sample Count

3. ACTUAL COUNT Each member of a population is counted one by one
Name of Population
Ducks
Cattails
Water Lilies
Actual Count 6 20 4
Sample Count

4. Which population was easiest to count?
Why?

5. RANDOM SAMPLES Make a GRID
Count the total number of squares in the grid
Choose one square of the grid at random.
Count the population in that one square.
Estimate the total population by multiplying the number in one square time the total squares in the grid.

6. RANDOM SAMPLES Name of Population Ducks Cattails Water Lilies
Actual Count 6 20 4
Sample Count
1 x10 = 10
3 x 10 = 30
1 x 10 = 10

7. ACCURACY???
Scientists help prevent over- and under-estimation by taking several samples and averaging the results.

8. QUESTIONS Why is a sample a good way to count a population?
What are some disadvantages to using a sample?
What could you do to sample a population of animals that do not stay in one place?