Nigel Holt and Rob Lewis - Crown House Publishing.

More documents

Recommendations

Info

20 | A2 PSYCHOLOGY: THE STUDENT’S TEXTBOOKFrequency polygonNumber of push-upsNUMBER OF PUSH-UPS POSSIBLE AT DIFFERENT MASS35.031.528.024.521.017.514.010.57.03.5050 100 150 200Mass (kg)The frequency polygon is very similar to the histogram.Imagine a histogram with a point drawnin the centre of the top of each bar. Now, removeall the bars and join up the points. A frequencypolygon has:»»A continuous variable on the x-axis»»A continuous line, no bars.TablesThe whole point of a table is to present otherwisecomplicated information in as simple a way aspossible. A table should allow readers to find theinformation they need with as little effort as possible.Tables can be large, containing lots of data,or they may be small, containing data in the formof summary statistics, such as mean, mode andmedian. In the case below, we have a table showingthe mean scores of male and female studentsin maths, English and science examinations.MathsEnglishScienceMale564351Female446752When drawing a table make sure you follow themost important rule: be as clear and straightforwardas you can.Which is best?Each measure of central tendency and dispersion has its good and bad points. A strong descriptive statistic isgenerally one that takes in a good deal of the raw data in its calculation, so bear that in mind when thinkingabout which is most suitable. The strengths and weaknesses of each are described below.StrengthWeaknessMeanMost powerfulmeasure ofcentral tendencyas it usesall of the dataOne roguescore (largeor small) canheavily influenceit. Forinstance, themean of 3, 4and 8 is 5. Themean of 3, 4,8 and 1,005is 255. Theextreme valuehas seriouslyinfluenced themeanModeThe bestmeasure to useif you wantto know howoften thingshappenSometimes adata set doesnot have amost commonvalue andsometimesit has lots ofcommon valuesMedianNot heavilyinfluenced byrogue scoresNot good forusing withsmall data sets.For instance, ifyou only havethe numbers 1,17 and 2,000in your dataset the medianis 17. Not veryinformativeStandarddeviationUses everyvalue in thedata set,not heavilydistorted byextreme valuesand is the mostsensitiveThe mostlaborious ofthe measuresof centraltendency tocalculateRangeTakes extremescores intoconsiderationand is simple tocalculateIf either of thetwo scores areextreme, rangewill be distorted.It tellsus little abouthow spread outor clusteredtogether thedata areSemiinterquartilerangeLess distortedscores than therangeUses only 50%of the data inthe calculationand is quitelaborious tocalculateIt’s not really useful to ask which of the measures is best and which is worst. Each is appropriate in differentcircumstances, depending on the data you have and what you are looking for in your research.Extract from A2 Psychology: The Student’s Textbook © Nigel Holt and Rob Lewis ISBN: 9781845901004 www.crownhouse.co.uk
DATA ANALYSIS AND REPORTING INVESTIGATIONS | 21Descriptive statisticsDescriptive statistics are ways of representingraw data simply. Measures of central tendencyand measures of dispersion are the two types ofdescriptive statistic with which you are familiarfrom your AS studies.A measure of central tendency is sometimesreferred to as an average. An average is the scorethat is typical of all the data you have in your set.Measures of dispersion tell us how spread out thedata are. The larger the measure of dispersion, themore spread out the data.Each measure of central tendency (mean, medianand mode) has an appropriate measure of dispersion:this is easily described in a table.“when using a ….Mean ….Median ….Mode ….use a ….”Standard deviationSemi-interquartile range,or rangeRangeCalculating these values is not very difficult: it justtakes a little time. This is how you make the calculations.It is worth refreshing your memory.Mean1. Add up the numbers in your data set (call thisnumber A).2. Count up the number of values in your dataset (call this number B).3. Divide A by B.Mode1. Identify the most common value in your dataset. This is the mode.2. If there are two equally common numbers youhave a ‘bi-modal’ set (2 modes).3. If you have three equally common numbersyou have a ‘tri-modal’ set (3 modes).Median1. Put your data in order (smallest to largest).2. The data value in the middle is the median.3. If you have an even number of values, take themean of the two in the middle.Standard deviation1. Calculate the mean of the values in your dataset.2. Subtract the mean from each value in turn andsquare the result in each case.3. Add up all of the squared values from step 2.Mathematical symbols – a handy guideThe problem with maths is that it sometimes uses symbols that make it look more like Ancient Greek thansomething we might possibly understand. It’s not that complicated actually. Here’s a handy guide to whateach symbol means.Symbol√∑Nxx2s=~Meaningsquare rootsigma. This just means ‘the sum of’the number of items in your data setthe value you are working withx-bar. This just means ‘the mean of your data set’multiply by itself. Also known as ‘squared’.lower case sigma. This means standard deviationequals. What’s on the left of the symbol equals what is on the rightless than. What’s on the left is less than what’s on the rightgreater than. What’s on the left is greater than what’s on the righta lot less than. What’s on the left is a great deal less than what’s on the righta lot greater than. What’s on the left is a lot greater than what’s on the rightapproximately. What’s on the left is approximately the same as what’s on the rightExtract from A2 Psychology: The Student’s Textbook © Nigel Holt and Rob Lewis ISBN: 9781845901004 www.crownhouse.co.uk
Page 1 and 2: Sample chapter:Psychological Resear
Page 3: the application of scientific mETHO
Page 6 and 7: 6 | A2 PSYCHOLOGY: THE STUDENT’S
Page 8: 8 | A2 PSYCHOLOGY: THE STUDENT’S
Page 11 and 12: DESIGNING PSYCHOLOGICAL INVESTIGATI
Page 19: DATA ANALYSIS AND REPORTING INVESTI
Page 23 and 24: DATA ANALYSIS AND REPORTING INVESTI
Page 41: DATA ANALYSIS AND REPORTING INVESTI

Nigel Holt and Rob Lewis - Crown House Publishing.

Create successful ePaper yourself

Delete template?

Save as template?