Random sampling

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Random Sampling
Sampling is needed to measure organisms- not every single organism can be counted so we use a system.
Sampling needs to be reliable: if repeated, the same/similar results will be obtained.
Sampling needs to be representative of a population- accurately reflect members of the population.
Random sampling removes bias from an investigation. Avoiding bias ensures that the data obtained are valid.
Counting daisies and buttercups
Equipment: Pen, paper, calculator, quadrat
Method: Use the random number generator function on the calculator. This number is the number of steps you will
take. Spin the pen to see which direction to head. If you reach the boundary, reflect off at the same angle you hit it.
Place the quadrat where you stop and count the number of daisies and buttercups. Input the data on a suitable table.
Take a minimum of 10 measurements per group.
When all the data has been gathered, input the class results onto a spreadsheet. Work out the running mean for
daisies and buttercups.
Running mean: moving average. You stop sampling when the running mean stabilises.
Using axis: form an axis from two tape measures (place at right angles), use the random number generator on the
calculator to establish coordinates. Each person goes to the appropriate grid reference then walks until the point
they meet. Place the quadrat and count daisies and buttercups.


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