James Ball, data journalist, the Guardian

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James Ball, data journalist, the Guardian

  1. 1. DON’T KILL THE audience <ul><li>WHY JOURNALISTS NEED DATA – </li></ul><ul><li>AND data needs journalists </li></ul>
  2. 2. statsitis <ul><li>A terrible new diseases – statsitis – affects 1 in 1,000 people. It is always fatal. Thankfully, it’s treatable. </li></ul><ul><li>The treatment always cures you if you’ve got statsitis . But if you haven’t and take the treatment, it’ll make you REALLY ill. </li></ul><ul><li>There is a test, 95% accurate , that will tell you if you have it. </li></ul><ul><li>You take the test. You test positive. Who wants treatment? What’s the chance you’ve got statsitis? </li></ul>
  3. 3. USE AND ABUSE OF STATS
  4. 4. REALLY? <ul><li>How much does a slice of bread weigh? </li></ul><ul><li>… what about a pizza base? </li></ul><ul><li>… what about cheese? </li></ul><ul><li>… meat? </li></ul><ul><li>… tomato? </li></ul>
  5. 5. use and abuse of stats
  6. 6. REALLY? <ul><li>INCOME: £2,000 / month </li></ul><ul><li>OUTGOINGS: £2,050 / month (including rent, debt, etc) </li></ul><ul><li>DEFICIT: = £2,050 - £2,000 = £50 / month </li></ul><ul><li>DEBT: £20,000 </li></ul><ul><li>I cancel my £20 / month gym membership. Do I need to cut another £30, or £19,800? </li></ul>
  7. 7. use and abuse of stats
  8. 8. REALLY? <ul><li>MEDIAN FULL-TIME INCOME (UK): £26,000 </li></ul><ul><li>TAX ON £26,000: £3,905 </li></ul><ul><li>A significant % of people don’t work, or work part time. </li></ul><ul><li>So how, exactly, are we paying £4,000 each for pensions? </li></ul>
  9. 9. USE AND ABUSE OF STATS
  10. 10. REALLY? <ul><li>Highest ever TV audience: 1.1bn </li></ul><ul><li>Actual (est) wedding audience: 300m </li></ul><ul><li>....we all do it sometimes. </li></ul>
  11. 11. REMEMBER THIS? <ul><li>A terrible new diseases – statsitis – affects 1 in 1,000 people. It is always fatal. Thankfully, it’s treatable. </li></ul><ul><li>The treatment always cures you if you’ve got statsitis . But if you haven’t and take the treatment, it’ll make you REALLY ill. </li></ul><ul><li>There is a test, 95% accurate , that will tell you if you have it. </li></ul><ul><li>You take the test. You test positive. Who wants treatment? What’s the chance you’ve got statsitis? </li></ul>
  12. 12. Here comes the science part <ul><li>A 95% accurate test will get it wrong 5 times out of 100 . </li></ul><ul><li>So for 1,000 people, 5% x 1,000 = 50 will test positive. Of those, only 1 is ill . </li></ul><ul><li>So if test positive, you have only a 1 in 50 = 2% chance of having the illness. </li></ul><ul><li>What does that mean in real life? </li></ul>
  13. 13. Who else gets this wrong? <ul><li>The example just given was based on a real study performed on a group of professionals. </li></ul><ul><li>The first time this was carried out (Eddy, 1982), 95% of professionals over-estimated by a factor of ten </li></ul><ul><li>They thought a positive result meant a 75% chance of having the illness. In reality, it was 7.7% </li></ul><ul><li>They were all doctors. </li></ul>

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