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An Introduction to Field Data Collection - Part 1
Part 1: Counting the Uncountable

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Problem: How many holes are in the ceiling tiles in this room?

Introduction: As you can see, the number of holes is quite large. How long would it take you to count all the holes in the tiles?

Materials: Meter stick or metric tape .1 x .1 m grid cutout

Researchers often run into problems of this type. The usual way is to start small. While it might be hard to count the number of holes in one .6 x 1.2 m tile, the number of holes in a .1 x .1 m patch is much smaller. Samples often consist of nested quadrats that may include areas of 1 km square on down through hectare to Meter Square and even down to smaller dimensions. (In microbiology the area may shrink to square micrometer.)

In any measurement problem there are limitations to what we can do. In this case, the problem is how high of a number is it practical to count. A good rule of thumb is to be sure the area you intend to count has a number of items no higher than 250. When you design an experiment of this type, the size of a sample plot is best set so that the number of individual items counted averages less than 250 in any plot. The plots should be set out in one of several methods designed to produce a random spread of sample points. The method we will use requires each lab group to move along an individual transect line recording sample results at intervals of one meter. At each sample point you will use a .1 x .1 m cutout to mark off a section of tile to count. Record your observations of the appearance of the sample site. Count only the holes within the grid and record the position number and the count in a table. Repeat the process at nine other points if time permits.

Measure and record the room dimensions. Calculate the area of the classroom ceiling.

Transect number_____________

Plot # # of holes Observations

Average number of holes____________

Room dimensions__________x__________ Area______________

Discussions Questions/Extensions ......
Use the data in your table to find an average number of points in .01 square meters and report your data and findings to the class recorder.

Is there a large difference or a small one between data points and the average?

Why is the count different?

Does your method account for areas not covered by tile?

Using the class data, calculate the class average number of holes / square meter. (Be sure to include a copy of the class data here)

Is the class data or average different than your average value?

By what percent is the class average different than your average count?

Is the difference significant?

What is the total number of holes in the classroom ceiling?

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