ao3

• when investigating sleep pattern, p's must be subjected to a specific level of control and attached to a monitor to measure rhythms. may appear invasive for p' which then leads to them sleeping in a way that does not represent their ordinary sleep cycle. lacks ecological validity -> false conclusions being drawn.
• however carried out in a controlled lab setting meaning the differences in sleep patterns could not be attributed to situational factors only to biological differences.
• individual differences: (tucker) found significant differences between p's in terms of the duration of each stage. suggesting that there may be innate individual differences in ultradian rhythms meaning it is worth focusing on these differences during investigations into sleep cycle