General Certificate of Education Advanced Level Examination June 2013

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1 General Certificate of Education Advanced Level Examination June 2013 Human Biology HBI6T/P13/task Unit 6T A2 Investigative Skills Assignment Task Sheet Investigation into whether reaction time is different using dominant and non-dominant hands Introduction A person s reaction time is the time it takes them to react to a stimulus. In this investigation you will find out how quickly someone reacts to seeing a ruler being dropped. How far the ruler falls before they catch it allows their reaction time to be found. You will investigate whether there is any difference between reaction times when using the dominant and non-dominant hand. A person s dominant hand is the hand that a person usually uses for writing. Materials You are provided with: l a metre ruler or half metre ruler l a pencil l access to a table or bench top l access to a chair or stool. You may ask for any other apparatus you require. In this Task Sheet there is a conversion chart for you to use at Stage 2 to convert distances fallen by the metre ruler to reaction times. A copy of the AQA Students Statistics Sheet is provided at the back of this Task Sheet. This may be used at any stage during the investigation and Written Test.

2 2 Outline method Read these instructions carefully before you start your investigation. In this investigation you will be working with a person chosen by your teacher. 1. Ask the person to draw a pencil line down the centre of each thumbnail (see diagram below). 2. Ask the person to sit sideways at the table or bench with the hand normally used for writing on the side nearer the table or bench. 3. Ask the person to place the forearm flat on the table with the hand over the edge and with the thumb and first finger approximately 2 cm apart. 4. Hold the ruler near the top and stand in front of the person. 5. Carefully move the ruler so that it is hanging vertically between the person s thumb and first finger with the zero opposite the pencil line on the person s thumbnail. Check that the ruler is not touching the person s thumb or first finger. Before release (step 5) When caught (step 7) Pencil line 6. Explain that when you let go of the ruler the person must catch it between thumb and first finger as quickly as possible. 7. Let the ruler go. When the person has caught it, record the measurement on the ruler that is nearest to the pencil line on the person s thumbnail. 8. Ask the person to turn round and sit with the other hand nearer the table or bench. 9. Repeat steps 3 to Repeat steps 2 to 9 with the same person until you have recorded at least 10 measurements for each hand. 11. Record your results in a suitable table on your Candidate Results Sheet: Stage 1. You will need to decide for yourself: l the number of measurements you make for each hand l which statistical test to carry out.

3 3 ISA HBI6T/P13 Candidate Results Sheet: Stage 1 Investigation into whether reaction time is different using dominant and non-dominant hands Centre Number Candidate Number Candidate Name... Record your data in a table in the space below. Hand in this sheet at the end of each practical session. (3 marks) 3 Turn over

4 4 ISA HBI6T/P13 Candidate Results Sheet: Stage 2 Investigation into whether reaction time is different using dominant and non-dominant hands Centre Number Candidate Number Candidate Name... Conversion Chart 1 Use the following chart to process your results, ie to convert distance fallen by ruler to reaction time in milliseconds. Record your processed results in the table on page 5. Distance fallen by ruler / cm Reaction time / ms Distance fallen by ruler / cm Reaction time / ms Distance fallen by ruler / cm Reaction time / ms

5 5 Record your processed results in the following table. Dominant hand Non-dominant hand Distance fallen by ruler / cm Reaction time / ms Distance fallen by ruler / cm Reaction time / ms (1 mark) Turn over

6 6 Analyse your data with a suitable statistical test. You may use a calculator and the AQA Students Statistics Sheet that has been provided. A sheet of graph paper has been supplied. You may use this if you wish. Hand in this sheet at the end of the practical session. 2 State your null hypothesis. (1 mark) 3 (a) Give your choice of statistical test. (1 mark) 3 (b) Give a reason for your choice of statistical test. (1 mark)

7 7 4 Carry out the test and calculate the test statistic. Show your working. (1 mark) 5 Interpret the test statistic in relation to your null hypothesis. Use the words probability and chance in your answer. (2 marks) 7 END OF QUESTIONS Turn over

8 8 This graph paper is provided for use if you need it. Hand in this sheet at the end of the practical session.

9 9 Students Statistics Sheet What sort of data did you obtain in your investigation? Measurements The investigation involved taking measurements Frequencies The investigation involved finding the number of individuals in particular categories Looking for associations between different measurements made from the same sample Looking for differences between measurements from different samples Looking for associations between measurements of two variables Chisquared (χ 2 ) test Spearman rank correlation Two sample t test Standard error and 95% confidence limits (Pearson s) correlation coefficient For use in the A2 ISA and EMPA assessment Turn over

10 10 Tables of critical values Statistical tests and tables of critical values A table of critical values is provided with each statistical test. If your calculated test statistic is greater than, or equal to, the critical value, then the result of your statistical test is significant. This means that your null hypothesis should be rejected. Spearman rank correlation test Use this test when l you wish to find out if there is a significant association between two sets of measurements from the same sample l you have between 5 and 30 pairs of measurements. Record the data as values of X and Y. Convert these values to rank orders, 1 for largest, 2 for second largest, etc. Now calculate the value of the Spearman rank correlation, r s, from the equation [ ] r s = 1 6 Σ D2 N 3 N where N is the number of pairs of items in the sample D is the difference between each pair (X-Y) of measurements. A table showing the critical values of r s for different numbers of paired values Number of pairs Critical value of measurements

11 11 Correlation coefficient (Pearson s correlation coefficient) Use this test when l you wish to find out if there is a significant association between two sets of measurements measured on interval or ratio scales l the data are normally distributed. Record the data as values of variables X and Y. Now calculate the value of the (Pearson) correlation coefficient, r, from the equation r = ΣXY [(ΣX)(ΣY)]/n {ΣX 2 [(ΣX) 2 /n]} {ΣY 2 [(ΣY) 2 /n]} where n is the number of values of X and Y. A table showing the critical values of r for different degrees of freedom Degrees of freedom Critical value Degrees of freedom Critical value For most cases, the number of degrees of freedom = n 2 Turn over

12 12 The t test Use this test when l you wish to find out if there is a significant difference between two means l the data are normally distributed l the sample size is less than 25. t can be calculated from the formula t = x 1 x 2 (s 1 2 /n 1 ) + (s 2 2 /n 2 ) where x 1 = mean of first sample x 2 = mean of second sample s 1 = standard deviation of first sample s 2 = standard deviation of second sample n 1 = number of measurements in first sample n 2 = number of measurements in second sample A table showing the critical values of t for different degrees of freedom Degrees of freedom Critical value Degrees of freedom Critical value The number of degrees of freedom = (n 1 + n 2 ) 2

13 13 Standard error and 95% confidence limits Use this when l you wish to find out if the difference between two means is significant l the data are normally distributed l the sizes of the samples are at least 30. For assessment purposes, five samples are acceptable providing that this is acknowledged either at a convenient place in the statistical analysis or in the conclusions. Standard error Calculate the standard error of the mean, SE, for each sample from the following formula: SE = SD n where SD = the standard deviation n = sample size 95% confidence limits In a normal distribution, 95% of datapoints fall within ± 2 standard deviations of the mean. Usually, you are dealing with a sample of a larger population. In this case the 95% confidence limits for the sample mean is calculated using the following formula 95% confidence limits = x ± 2 SD OR x ± 2 SE n Turn over

14 14 Use this test when The chi-squared test l the measurements relate to the number of individuals in particular categories l the observed number can be compared with an expected number which is calculated from a theory, as in the case of genetics experiments. The chi-square (χ 2 ) test is based on calculating the value of χ 2 from the equation χ 2 = where O represents the observed results E represents the results we expect. Σ (O E) 2 A table showing the critical values of χ 2 for different degrees of freedom E Degrees of Critical value freedom The number of degrees of freedom = number of categories 1 Copyright 2013 AQA and its licensors. All rights reserved.

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