# BALA201 Lecture notes

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BALA201 LECTURE NOTES Topic 3 Descriptive statistics Descriptive statistics refers to methods of describing and summarising data using tabular, visual and quantitative techniques. Metrics and data classifications: Metric - "a unit of measurement that provides a way to objectively quantify performance". Measurement - the act of obtaining data associated with a metric. Measures - numerical values associated with a metric. Metrics can be DISCRETE or CONTINOUS - Discrete: from counting something e.g., number of errors - Continuous: on a continuous scale e.g., length, weight Data classifications (measurement scales) categorical ( nominal ) data - sorted into categories according to specified characteristics. ordinal data - can be ordered or ranked. interval data - ordered, with constant differences between observations and many have arbitrary zero points. ratio data - continuous and have a natural zero. Scaling e.g. Nominal - numbers assigned to runners. Ordinal - rank order of winners Interval - performance rating on a 0-10 scale Ratio - time to finish in seconds.
BALA201 LECTURE NOTES Frequency distributions & histograms
BALA201 LECTURE NOTES Freq distribution: a table showing number of observations in each group. Histogram: a column chart of a frequency distribution groups must not overlap. Relative frequency distributions Relative frequency is the fraction (proportion) of the total number of observations in a group (often expressed as %) If a data set has n observations: Relative frequency of category i = frequency of category i/n Relative frequency distribution is a table showing the relative frequency of each group.