General Certificate of Education Advanced Level Examination June 2010

Transcription

1 Genera Certificate of Education Advanced Leve Examination June 2010 Human Bioogy HBI6T/Q10/task Unit 6T A2 Investigative Skis Assignment Task Sheet The effect of using one or two eyes on the perception of distance Introduction In this investigation, you wi attempt to drop a counter into a sma container. You are going to investigate how using one or two eyes affects your abiity to judge distance. You wi measure your abiity to judge distance with one eye open and with two eyes open. It is important that you do not practise any of the steps in this investigation before starting work. You wi need to make some decisions for yoursef. Materias You are provided with 10 pastic counters a sma container with a thin ayer of cotton woo at the bottom a cear, fat surface to work on a ruer or tape measure You may ask your teacher for any other apparatus you require.

2 2 Outine Method Read these instructions carefuy before you start your investigation. 1. Pace the container on the cear, fat surface. There shoud be nothing ese on the surface. 2. Sit down facing the surface with both hands on your ap. 3. Take the container in one hand and then cose both your eyes. Side the container to a pace over 30 cm from you. Remove your hand from the container and repace it on your ap. 4. Open one eye and use your other hand to pick up a counter. 5. Hod the counter at eye eve, and immediatey try to drop the counter into the container. 6. Record a hit or a miss. 7. Repeat steps 3 to 6 by moving the container to another position. 8. Repeat steps 3 to 7 as many times as necessary to carry out a suitabe statistica test. 9. Repeat steps 3 to 8 but this time drop the counter with both eyes open. You wi need to decide for yoursef what is a hit and what is a miss how many repeats to do which statistica test to carry out.

3 3 ISA HBI6T/Q10 Candidate Resuts Sheet: Stage 1 The effect of using one or two eyes on the perception of distance Centre Number Candidate Number Candidate Name... Record your data in a tabe in the space beow. (2 marks) Hand in this sheet at the end of each practica session. Turn over

4 4 ISA HBI6T/Q10 Candidate Resuts Sheet: Stage 2 The effect of using one or two eyes on the perception of distance Centre Number Candidate Number Candidate Name... Use the space beow to anayse your data with a suitabe statistica test. You may use a cacuator and the statistica sheet that has been provided to perform this test. (6 marks) You shoud state your nu hypothesis give your choice of statistica test give reasons for your choice of statistica test

5 5 carry out the test and cacuate the test statistic interpret the test statistic in reation to the nu hypothesis being tested. Turn over

6 6 This graph paper is provided for use if you need it. Hand in this sheet at the end of the practica session.

7 7 Students Statistics Sheet What sort of data did you obtain in your investigation? Measurements The investigation invoved taking measurements Frequencies The investigation invoved finding the number of individuas in particuar categories Looking for associations between different measurements made from the same sampe Looking for differences between measurements from different sampes Looking for associations between measurements of two variabes Chisquared (χ 2 ) test Spearman rank correation Two sampe t test Standard error and 95% confidence imits (Pearson s) correation coefficient For use in the A2 ISA and EMPA assessment Turn over

8 8 Tabes of critica vaues Statistica tests and tabes of critica vaues A tabe of critica vaues is provided with each statistica test. If your cacuated test statistic is ess than, or equa to, the critica vaue, then the resut of your statistica test is significant. This means that your nu hypothesis shoud be rejected. Spearman rank correation test Use this test when you wish to find out if there is a significant association between two sets of measurements from the same sampe you have between 5 and 30 pairs of measurements. Record the data as vaues of X and Y. Convert these vaues to rank orders, 1 for argest, 2 for second argest, etc. Now cacuate the vaue of the Spearman rank correation, 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 sampe. D is the difference between each pair (X-Y) of measurements. A tabe showing the critica vaues of r s for different numbers of paired vaues. Number of pairs Critica vaue of measurements

9 9 Correation coefficient (Pearson s correation coefficient) Use this test when you wish to find out if there is a significant association between two sets of measurements measured on interva or ratio scaes the data are normay distributed. Record the data as vaues of variabes X and Y. Now cacuate the vaue of the (Pearson) correation 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 vaues of X and Y. A tabe showing the critica vaues of r for different degrees of freedom. Degrees of freedom Critica vaue Degrees of freedom Critica vaue For most cases, the number of degrees of freedom is = n 2 Turn over

10 10 The t test Use this test when you wish to find out if there is a significant difference between two means the data are normay distributed the sampe size is ess than 25. t can be cacuated from the formua t = x 1 x 2 (s 1 2 /n 1 ) + (s 2 2 /n 2 ) Where x 1 = mean of first sampe x 2 = mean of second sampe s 1 = standard deviation of first sampe s 2 = standard deviation of second sampe n 1 = number of measurements in first sampe n 2 = number of measurements in second sampe A tabe showing the critica vaues of t for different degrees of freedom. Degrees of freedom Critica vaue Degrees of freedom Critica vaue The number of degrees of freedom = (n 1 + n 2 ) 2

11 11 Standard error and 95% confidence imits Use this when you wish to find out if the difference between two means is significant the data are normay distributed the sizes of the sampes are at east 30. For assessment purposes, five sampes are acceptabe providing that this is acknowedged either at a convenient pace in the statistica anaysis or in the concusions. Standard error Cacuate the standard error of the mean, SE, for each sampe from the foowing formua: SE = SD n Where SD = the standard deviation n = sampe size 95% confidence imits In a norma distribution, 95% of datapoints fa within ± 2 standard deviations of the mean. Usuay, you are deaing with a sampe of a arger popuation. In this case the 95% confidence imits for the sampe mean is cacuated using the foowing formua 95% confidence imits = x ± 2 SD OR x ± 2 SE n Turn over

12 12 Use this test when The chi-squared test the measurements reate to the number of individuas in particuar categories the observed number can be compared with an expected number which is cacuated from a theory, as in the case of genetics experiments. The chi-square (χ 2 ) test is based on cacuating the vaue of χ 2 from the equation χ 2 = Σ (O E) 2 E Where O represents the observed resuts E represents the resuts we expect. A tabe showing the critica vaues of χ 2 for different degrees of freedom. Degrees of Critica vaue freedom The number of degrees of freedom = number of categories 1 Copyright 2010 AQA and its icensors. A rights reserved.