Quantitative investigations of variation within a species involve: collecting data from random samples; calculating a mean value and the standard deviation of that mean; interpreting mean values and their standard deviations
Scientists measure variation within a species by taking random samples and calculating two statistics. The mean shows the average value, and the standard deviation shows how spread out the data are around that average.
Formula
Standard deviation = √(Σ(x − x̄)² / (n − 1))
Real World
A sixth-form class measuring daisy stem heights on the school field used random-number coordinates on a grid to place quadrats, then found a mean of 8.2 cm with SD of 1.1 cm — the small SD showed most daisies grew to a similar height in that habitat.
Exam Focus
If two means overlap within ±1 SD, state there is no significant difference — examiners reward correct interpretation over calculation.
Evaluation Scaffold
A four-step framework for high-quality evaluation. Use this for 'assess', 'evaluate', and 'to what extent' questions.
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