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Effects of Caffeine on Reaction Time

Paper Type: Free Essay Subject: Physiology
Wordcount: 1796 words Published: 18th May 2020

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The SACE approved investigation was conducted to investigate the effects of caffeine on reaction time.

It was hypothesized that those participants in the fully caffeinated group would have better reaction times than those in the decaffeinated group. This hypothesis was chosen based on previous knowledge on the effects of caffeine – it is a stimulant that speeds up communication between the nervous system and the brain, resulting in less fatigue and better concentration.

Caffeine is one of the most widely used legal drugs in the world today. It is relatively rare to find a non-coffee drinker and going out for coffee is one of the most common social outings. It is relied upon by millions of people to wake themselves up every morning, to keep them going throughout a long day, to stay awake when driving late at night. Researching the effects of caffeine on reaction time allows scientists to create accurate predictions without relying on subjective opinions or advertising campaigns. It could debunk any myths and expose any placebo effects. This could be useful for many people, such as truck drivers who use caffeine to keep their reactions sharp when they are feeling fatigued

This is an experimental investigative design that will generate objective quantitative data. An online reaction test was used to measure the reaction time of participants. In the report, the three groups (100% caffeine, 50% caffeine and 0% caffeine) will be compared using a variety of graphs and tables.

Data Analysis

The 0% group had a mean score of 0.39 seconds and a range of 0.394. The 50% group had a mean score of 0.40 and a range of 0.339. The 100% group had a mean score of 0.365 and a range of 0.292. From these values we can see that the change in reaction time is too small to be significant, but the change in range has a definite trend line.

Causes of this inconsistency could include the very small sample size, the type of reaction test used and if anyone had consumed caffeine prior to the experiment.

Overall, the data does not provide a solid conclusion and is not precise, however it does support the hypothesis as the 100% caffeinated group has the lowest mean and range.


The purpose of this experiment was to observe whether caffeine affects reaction time and the hypothesis that has been tested is that caffeine increases reaction time.


Figure 1: Mean score and range results of reaction time test graphed


  • Interpreting

The mean score of the treatment group is slightly lower than that of the control group, showing there is a change however it is a very minimal difference. However, the range of the results shows that there is in fact a noticeable difference in reaction time, differing by approximately 0.1 seconds. From this, it can be concluded that the more caffeine that is consumed, the faster the reaction time will be. An issue with this experiment was that the class was largely female, which will not give a statistic that is accurate for the general population.

  • Evaluating

This was a single blind experimental investigation as the participants were blind to the group they were in and amount of caffeine consumed, however the investigator was not blind to this. The sample was randomly collected by the subjects drawing a piece of paper with a number and a colour out of a bag. The number and colour that was on the piece of paper represented which group the participant was in. The data that was collected does not represent the vast population as the entire experiment consisted of teenagers that were generally of the same age which means adults and/or younger children may not respond in the same way or may have better or worse results than what was collected. The data collected also does not represent the population as the class was mostly female, meaning the experiment was heavily gender biased. Sampling also affects the reliability of the results as either all or none of the participants could have been avid coffee drinkers. If this were the case, those that were avid coffee drinkers’ reaction times may not have changed as that is what their performance would be on a regular basis. Either way, a larger sample is required if the results are to not be influenced by the personal status of each participant. It is certain that there are many undesirable variables that can influence the results of the experiment. A factor that could have a large impact on the reaction time of a participant is their attitude as they may not have been interested in the experiment which would make their reaction time much slower regardless of the amount of caffeine consumed. Another factor that may also have an influence is the environment in which the experiment was conducted as some may have felt more comfortable than others. Other factors, which are known as confounding variables, such as intelligence, gender, or age could also affect the reaction time [2]. The time of day could also have had an effect on results as the effects of caffeine are more pronounced in the morning rather than the afternoon.

  • Strengths of the investigation

A strength of this investigation included it being objective quantitative which entails that the results consider no subjective bias. A big strength of this investigation is that it is an experimental design which means cause and effect can be established by deliberately manipulating one variable, in this case the amount of caffeine consumed, whilst keeping every other variable the same. Another strength was that the investigation itself is easy to replicate. The investigation should be replicated multiple times with many different types of people as the results cannot be generalised from a single experiment. The more often an experiment is repeated, the more accurate the results will be [4]. The control group is intended to allow us to conclude that it is in fact the independent variable that is influencing the dependant variable.

  • Weaknesses of the investigation

A weakness of this experiment is that some people could have had coffee earlier in the day which would skew the results, potentially making their reaction time even faster or even reduced the effects of the caffeine as a whole. Some people could have also practiced the reaction time test beforehand even though they were told otherwise, meaning they would know what to expect when the time came for the participant to do the said test. Another thing is that the artificiality of the setting would also produce unnatural behaviour which would mean it may not be possible to generalise the findings to a real-life setting [1]. By only doing one type of test, in this case the online reaction time test, it does not give us a definitive answer as to whether or not it does actually increase reaction times. Another test that could have been conducted is to see how fast the individual can react to a ball being thrown at them, or someone could have dropped a ruler, placing the bottom of the ruler in the palm of the participant, then dropping it and seeing how fast they can catch it. A big weakness of the investigation is that no testing done beforehand meaning we do not actually have an idea of whether or not the reaction time of the participants actually increased. Another weakness of the investigation is something called demand characteristics, where the participants are aware of the experiment and what the investigator is after so their behaviour may change [3].

  • Improvements

One improvement to this experiment would be to have a larger sample size as 19 participants is not enough to generalise the results across the general population. Another improvement would be to have more males and those that are of different ethnic backgrounds as those may affect the results.

  • How were ethics considered in the investigation?

As for ethics, the participants were briefed and debriefed properly, there was voluntary participation, informed consent was given, the participants were informed that they had the right to withdraw, and those that were lactose intolerant were not given milk. However, it is to be taken into consideration that there was inaccurate recording of the data. It was found that for group 3, the male results were divided by two when there was only one entry meaning there was an incorrect value when graphing the results. It was also found that there were five entries for males when there were only three participating in the investigation.


In conclusion, the hypothesis was accepted as it was found that caffeine increases reaction time. Most ethics were taken into consideration and the experiment was completed successfully.

Reference List

[1] McLeod, S. (2012). Experimental Method. Retrieved from https://www.simplypsychology.org/experimental-method.html

[2] Experimental design: “Caffeine affects reaction time’. (2015). Retrieved from https://elisabeth-carrio.com/experimental-design-caffeine-affects-reaction-time/.

[3] Experiments. (n.d.). Retrieved from https://www.s-cool.co.uk/a-level/psychology/research-methods/revise-it/experiments.

[4] Advantages and disadvantages of experiments. (n.d.). Retrieved from http://www.holah.karoo.net/evaluationofexperiment.htm.


Group 1 (0%)

Group 2 (50%)

Group 3 (100%)

Mean Score









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