Information about Statistics-Presentation-Public-Edition

Published on July 28, 2014

Author: andrewburkert3



STORIES AND STATISTICS: STORIES AND STATISTICS PowerPoint Presentation: Prepared by Frank Swain National Coordinator for Science Training for Journalists Royal Statistical Society [email protected] 020 7614 3947 Contents: Communicating numbers Percentages & percentage points Surveys Averages Uncertainty Trends Correlation versus causation Probabilities: what makes a value unusual ? Absolute and relative risk Imagery Contents PowerPoint Presentation: Communicating numbers #1 Breaking down big numbers: Breaking down big numbers Your numbers are characters in the story – give them some personality Breaking down big numbers: Breaking down big numbers “1.4 million photos are uploaded a second” 1.4m photos x 86,400 seconds in a day ÷ 500 million users = 240 photos per person per day Realistic? PowerPoint Presentation: Numbers often need to be scaled to be meaningful e.g. per person, per passenger mile etc. Hospitals Tourist info centres Putting numbers in context PowerPoint Presentation: “The implant has been used by around 1.4 million women since it was introduced in 1999. In its 11 years of use, medicine regulators have recorded 584 pregnancies among users” “…for every 1,000 women using it, less than one will get pregnant over a three-year period” Putting numbers in context Percentages: Percentages Percentages less than 1% are difficult to interpret. Better to use “3 in every 10,000” than 0.03% Also be careful with percentages bigger than 100% - can be better to use double, triple etc. PowerPoint Presentation: Know the difference between a percentage and a percentage point . VAT increased to 20% on January 2011 This is a rise of 2.5 percentage points not a rise of 2.5% Percentages PowerPoint Presentation: = 1 million smokers = 1 million non-smokers 1948 1970 UK smoking rate 26m smokers 25m smokers “The smoking population shrank by 4 per cent” 65% 55% “The smoking rate has declined 10 percentage points” PowerPoint Presentation: Surveys #2 What’s been counted?: What’s been counted? How many… ballot papers? chairs? hearts beating? footprints? …people? Polls and surveys: Polls and surveys Polls are ways of finding out what a population thinks without asking everyone Sample size – poll of 1000 people has ± 3% confidence interval just from sampling So be careful of small subgroups of the sample, 100 people gives ± 10% Survey example: Survey example “…couples now expect to blow an average of £20,273 tying the knot…” Which average? Whose wedding? Who’s asking? PowerPoint Presentation: Do you have the exact questions the pollster asked? Are they precise and fair? #3 Polls and surveys: Polls and surveys Do the people surveyed reflect the wider population? ( selection bias) Were the questions asked in a fair way? ( response bias) Who commissioned the survey? Statistical significance: Statistical significance So how do we know if an event really is interesting or if it was just random variation ? That’s what ‘statistical significance’ is about. For example, is a cluster of cancer cases in an area suspicious or likely to be just natural variation? League tables: League tables League tables are often meaningless because the natural variation is far bigger than the differences in the table PowerPoint Presentation: There are many different ways of calculating an average . Which is the appropriate one to use? #4 Variation and distributions: Variation and distributions We often want to summarise a distribution of values with one number – an average. But there are different types of average: mean , median and mode . PowerPoint Presentation: Average does not mean the same thing as typical. Different averages tell different stories – say which you are using . Averages Averages: Averages Mode, £275 Median, £377 Mean, £463 PowerPoint Presentation: Bottom line: Give an idea of the size and shape of the spread around the average. Averages Normal distribution: Normal distribution 95.4% 68.2% PowerPoint Presentation: A WORD ON “AVERAGE” PowerPoint Presentation: How accurate are the figures ? #5 PowerPoint Presentation: “The number of people out of work rose by 38,000 to 2.49 million in the three months to June, official figures show.” GOLDACRE: “The estimated change over the past quarter is 38,000, but the 95% confidence interval is ± 87,000, running from -49,000 to 125,000. That wide range clearly includes zero, no change at all.” PowerPoint Presentation: One change in the numbers does not make a trend. Blips often happen. #6 PowerPoint Presentation: Trends PowerPoint Presentation: Trends PowerPoint Presentation: Beware spurious connections that don’t amount to ‘a causes b’. #7 Correlation and causation: Correlation and causation Correlation and causation: Correlation and causation Correlation and causation: Correlation and causation Correlation and causation: Correlation and causation A significant correlation between two variables does not imply one causes the other. Often there is a common cause for both variables, or it’s just a coincidence. PowerPoint Presentation: “Regression to the mean” The most abused correlation in the world! PowerPoint Presentation: “One in a million”. #8 Probability and coincidences: Probability and coincidences The chance of an event can be very small, but if it has lots of opportunities to happen, it can be near certain. Most weeks someone wins the lottery. Probability: Probability “the chances… an astonishing 48 million to one” Actually it’s only 133,000 to one… …and there are around 167,000 third children born in the UK each year. Always think about how many opportunities there were for a coincidence to happen Probability: Probability PowerPoint Presentation: Extremes PowerPoint Presentation: You should know what the absolute and the relative risk is, and communicate both. # 10 Risk: Risk Google tells me…. diabetes, weight gain, cigarette smoke, HRT, solariums …all “ double” my risk of cancer What, me worry? Risk example: But how bad is that? Risk example “B acon increases risk of colorectal cancer by 20 %” PowerPoint Presentation: About 5 out of 100 people develop colorectal cancer. Risk example PowerPoint Presentation: If all 100 ate 3 extra rashers every day... The number would rise to six Risk example PowerPoint Presentation: “Bacon increases risk of Colorectal cancer by 20%” Is therefore the same as saying So… “About 1 extra case per 100 people” Risk: Risk Absolute risk increases from 5% to 6% Absolute risk increases by 1 percentage point Relative risk increases by 20% 100 people eating 50g of processed meat every day for the rest of their lives would lead to 1 extra case of colorectal cancer PowerPoint Presentation: Apply the same rules to a graphic that you would a story: strive for accuracy, clarity and a strong narrative. # 11 Visualising data: Visualising data 2009 2010 2011 2012 2013 2014 2015 2020 2030 2040 Visualising data: Visualising data PowerPoint Presentation: Visualising data PowerPoint Presentation: Visualising data PowerPoint Presentation: Resources Royal Statistical Society

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