Notes

Outline

Statistics 1 The Basics Sherril M. Stone, Ph.D. Department of Family Medicine OSU-College of Osteopathic Medicine

What are Statistics? A set of methods and rules for organizing and interpreting data Alone a statistic can’t lie – it is what people do with statistics that leads to problems

Why Do I Need Stats? Statistics are a common part of everyday life crime rates average time of possession in a sports game different polls They answer questions Does a particular surgery really work? Is Treatment A better than Treatment B? Do smokers get lung cancer more than non-smokers?

Terms POPULATION - the entire group a researcher wishes to study SAMPLE - a subset of the population PARAMETER – a characteristic of a population VARIABLE - anything measured about the participants/subjects Dependent - what is measured, it is the outcome variable Independent - what the researcher manipulated or controlled a.  Quantitative (continuous) – amount, degree of the variable b.  Qualitative (categorical, nominal) - categories RAW DATA - the actual numbers collected Data is a plural noun Correct: The data are presented in Table 1 SAMPLE STATISTIC - a summary measure of the sample

Measurement Scales Nominal scale difference only, numbers have no quantitative value Ex: 1 = female, 2 = male Ordinal scale rank order, numbers are greater than or less than 1 = best, 2 = better, 3 = good Interval scale equal intervals, distance between numbers is equal Inch marks on a ruler Ratio scale true zero point, absence or presence of variable weight, height, temperature (Kelvin scale)

Types of Procedures Descriptive Statistics summary numbers computed on raw data Mean, Standard deviation, Variance, Correlation Inferential Statistics generalizations from sample to population t-test, ANOVA, Multivariate

Notations Variables and individual scores Capital letters, (X, Y) indicate variables The score for subject 4 would be written X4 Sums The upper case Greek sigma to indicate "the sum of" Lower case n for the number of subjects in a sample Upper case N for the number of subjects in population Raw data  X1 X2 X3 X4 3 5 1 2                       Note: the sample size is n = 4

Rounding General Rule - carry out all to four decimal places then round Above .50  round up 7.3369 rounds up to 7.34 7.3351 rounds up to 7.34 Below .50  round down 7.3328 rounds down to 7.33 7.3349 rounds down to 7.33 Exactly at .50  round to an even number. 7.3350 rounds to 7.34, up a bit 7.3450 rounds to 7.34, down a bit 7.3450001 rounds to 7.35, 50001 is slightly higher than .50. Exponential notation on calculators 3/524 = .00572519084 =  5.72519084 E-3 in exponential notation E-3 signifies that the decimal place is really three places to the left

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