Why should each participant complete several trials rather than one?

Reaction time varies from attempt to attempt, so a mean of several trials is a more reliable measure and anomalous results can be identified.

A ruler falls 30.0 cm before being caught. Using distance = ½ × 9.81 × time², calculate the reaction time.

Time = √(2 × 0.300 ÷ 9.81) = √0.0612 = 0.25 s.

The mean reaction time of a group in their twenties is 0.19 s and that of a group in their seventies is 0.27 s. Calculate the percentage increase.

The increase is 0.08 s, so the percentage increase is (0.08 ÷ 0.19) × 100 = 42%.

Why is a statistical test needed even when the mean reaction time of the older group is clearly higher?

The values within each group vary widely and overlap, so a test is needed to judge whether a difference between the means this large could reasonably have arisen by chance.

OCR A-Level Biology B H422

The Developing Cell: Cell Division and Cell Differentiation

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The Effect of Ageing on the Nervous System

Investigating ageing, reaction times and memory

3 things to know
Components 01, 02 and 03

Overview

Recall questions on comparing reaction times of age groups with a ruler drop test, calculating reaction times and percentage increases, null hypotheses and t-tests, word-list memory tests and their controls, ethics with elderly volunteers, confounding variables, and cross-sectional and longitudinal studies.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Describe how you would use a ruler drop test to compare the reaction times of two age groups.

Key term

Secondary data show mean hearing thresholds rising steadily with age in a sample of factory workers. Why should this not be attributed to ageing alone?

Key term

Give three variables that must be kept the same for every participant in a reaction time investigation.

Questions from this subtopic

Each one with the model answer underneath.

1
Describe how you would use a ruler drop test to compare the reaction times of two age groups.
Model answer
Each participant sits with the forearm supported and the ruler held vertically at the zero mark between their open thumb and finger, the ruler is released without warning and the distance caught is recorded, and several trials are averaged for each person before the group means are compared.
2
Give three variables that must be kept the same for every participant in a reaction time investigation.
Model answer
The hand used and the position of the fingers, the absence of any warning before the ruler is released, and the number of practice trials must be the same for everyone.
3
Why should each participant complete several trials rather than one?
Model answer
Reaction time varies from attempt to attempt, so a mean of several trials is a more reliable measure and anomalous results can be identified.
4
A ruler falls 30.0 cm before being caught. Using distance = ½ × 9.81 × time², calculate the reaction time.
Model answer
Time = √(2 × 0.300 ÷ 9.81) = √0.0612 = 0.25 s.
5
The mean reaction time of a group in their twenties is 0.19 s and that of a group in their seventies is 0.27 s. Calculate the percentage increase.
Model answer
The increase is 0.08 s, so the percentage increase is (0.08 ÷ 0.19) × 100 = 42%.
6
Why is a statistical test needed even when the mean reaction time of the older group is clearly higher?
Model answer
The values within each group vary widely and overlap, so a test is needed to judge whether a difference between the means this large could reasonably have arisen by chance.

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The Developing Cell: Cell Division and Cell Differentiation

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The Development of Species: Evolution and Classification

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