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Statistics Question Tell whether the following statement is true or false: Nominal measurement is the ranking of objects based on their relative standing on an attribute. Answer Nominal measurement: the classification of characteristics into mutually exclusive categories Ordinal measurement: the ranking of objects based on their relative standing on an attribute Measurement • Nominal measurement: the classification of characteristics into mutually exclusive categories • Ordinal measurement: the ranking of objects based on their relative standing on an attribute • Interval measurement: indicating not only the ranking of objects but the amount of distance between them • Ratio measurement: distinguished from interval measurement by having a rational zero point Descriptive Statistics • Summarize quantitative data • Describe quantitative data Question Tell whether the following statement is true or false: Frequency distributions impose order on raw data. Numeric values are ordered from lowest to highest, accompanied by a count of the number of times each value was obtained. Answer True Frequency distributions impose order on raw data. Numeric values are ordered from lowest to highest, accompanied by a count of the number (or percentage) of times each value was obtained. Frequency Distributions • Impose order on raw data. • Numeric values are ordered from lowest to highest, accompanied by a count of the number (or percentage) of times each value was obtained. • Common methods of display – Histograms – Frequency polygons Distribution • Symmetric: two halves are mirror images of each other • Skewed: Asymmetric with one tail longer than the other – Positively skewed – Negative skewed • Modality: number of peaks – Unimodal – Multimodal • Normal distribution Question What is the median? A. Average or typical value of a set of scores B. Value that occurs most frequently in a distribution C. Point above which and below which 50% of the cases fall D. Arithmetic average of all scores Answer C Central tendency are indexes, expressed as a single number, that represent the average or typical value of a set of scores. The mode is the value that occurs most frequently in a distribution, the median is the point above which and below which 50% of the cases fall, and the mean is the arithmetic average of all scores. Central Tendency • Central tendency are indexes, expressed as a single number, that represent the average or typical value of a set of scores. • Mode: value that occurs most frequently in a distribution • Median: point above which and below which 50% of the cases fall • Mean: arithmetic average of all scores Question Tell whether the following statement is true or false: Range is distance between the highest and lowest scores Answer True Range is distance between the highest and lowest scores. Variability • Variability: how spread out the data is • Range: distance between the highest and lowest scores • Standard deviation: indicates how much, on average, scores deviate from the mean • Calculation: – Deviation scores represent the degree to which each person’s score deviates from the mean. The variance is equal to the SD squared. Bivariate Descriptive Statistics • Relationships between two variables • Contingency table two-dimensional frequency distribution in which the frequencies of two nominal- or ordinal-level variables are crosstabulated. • Correlation coefficients describe the direction and magnitude of a relationship between two variables. – Product moment correlation coefficient (Pearson’s R)—interval or ratio – Spearman rho coefficient—ordinal • Scatter plot Risk Indexes • Absolute risk reduction: expresses the estimated proportion of people who would be spared from an adverse outcome through exposure to an intervention • Relative risk: expresses the estimated proportion of people who would be spared from an adverse outcome through exposure to an intervention • Relative risk reduction: estimated proportion of untreated risk that is reduced through exposure to the intervention Risk Indexes • Odds ratio: ratio of the odds for the treated versus untreated group • Number needed to treat: estimate of how many people would need to receive the intervention to prevent one adverse outcome