StatisticsStatistics

QuestionQuestion

Tell whether the following statement is true or false:

Nominal measurement is the ranking of objects based on their relative standing on an attribute.

AnswerAnswer

Nominal measurement: the classification of characteristics into mutually exclusive categories

Ordinal measurement: the ranking of objects based on their relative standing on an attribute

MeasurementMeasurement

• 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 StatisticsDescriptive Statistics

• Summarize quantitative data

• Describe quantitative data

QuestionQuestion

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.

AnswerAnswer

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 DistributionsFrequency 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 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

QuestionQuestion

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

AnswerAnswer

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 TendencyCentral 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

QuestionQuestion

Tell whether the following statement is true or false:

Range is distance between the highest and lowest scores

AnswerAnswer

True

Range is distance between the highest and lowest scores.

VariabilityVariability

• 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 StatisticsBivariate 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 IndexesRisk 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 IndexesRisk 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