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BASIC STATISTICS

BASIC STATISTICS. Prepared by Mrs Goh Cheng Wai. Why use statistics in research?. Organize and interpret data Description of data Mean, distribution of data Comparison of data Any significant difference between scores of different groups Relationship between two sets of data.

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BASIC STATISTICS

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  1. BASIC STATISTICS Prepared by Mrs Goh Cheng Wai

  2. Why use statistics in research? Organize and interpret data • Description of data • Mean, distribution of data • Comparison of data • Any significant difference between scores of different groups • Relationship between two sets of data

  3. Description of dataMeasures of central tendency • Mean – arithmetic average of a set of scores • Median – mid-point of a set of ordered scores • Mode – the most frequent value in a set of scores

  4. Description of dataMeasures of central tendency

  5. Description of dataMeasures of central tendency 1, 7, 2, 9, 6, 9 Mean = 5.7 Median = 6.5 1, 2, 6, 7, 9, 9 Mode = 9

  6. Description of dataMeasures of central tendency Mean = (6x1 + 7x2 + 8x5 + 9x3 + 10x2 + 11x2) 15 = 8.6 6, 7, 7, 8, 8, 8, 8, 8, 9, 9, 9, 10, 10, 11, 11 Median = 8 Mode =8

  7. Description of dataMeasures of spread of data • Consider these sets of data: • Group A – 11, 1, 3, 8, 4, 9 • Group B – 6, 7, 8, 6, 4, 5 • Both groups have the same mean of 6 • Data for group A is more widely spread around the mean • The standard deviation measures the spread of data around the mean

  8. 3 SD 2 SD 1 SD Description of dataMeasures of spread of data

  9. Comparison of data • You wish to find out the effect of milk on the growth rate of mice. • Experimental group: 10 mice fed with milk everyday • Control group: 10 mice not fed with milk • Measure the mass of each mouse once every week

  10. Comparison of data Start of experiment 10 weeks later 20 weeks later Experimental group Dependent t-test Independent t-test Control group Dependent t-test represents the mean mass of each group of mice

  11. t-test analysis • Independent t-test compares the means of two different groups • Dependent t-test compares the means of the same group at two different periods of time

  12. What is the t-test for? • After you have obtained the raw data, these questions may come to your mind: • Has milk really increased the growth rate of mice significantly over the control group? • How likely is the difference of mass between the two groups of mice due to chance?

  13. Finding significant differences • Difference in means between experimental and control group that occurs by chance MEANS THAT • Even if intervention is not applied, the difference still occurs

  14. What does the t-test p value mean? • Difference “by chance” observed more than 5 out of 100 times (p  0.05)  There is actually no significant difference between the two sets • Difference “by chance” observed less than 5 out of 100 times (p  0.05)  The two sets of data show significant difference

  15. Did milk increase growth rate of mice significantly?

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