Detailed notes
Distinguish primary/secondary data and census/sample. Specify population, variable and sampling method. Organise observations in frequency distributions, then select tables, bar or pie diagrams, histograms, frequency polygons, ogives or time-series graphs suited to the data.
Worked interpretation
A shop records daily sales of ₹120, ₹150, ₹150, ₹180 and ₹200. In ascending order the values are unchanged; range=₹200−₹120=₹80. A time-series line graph is appropriate for daily sales across a month because the order of dates matters. A histogram is for grouped continuous data, with adjoining bars.
CBSE-style practice
- A survey of 40 of 400 customers is a sample. Explain possible selection bias and choose a graph for monthly sales.
- Draw a labelled graph or table where it clarifies your reasoning.
- State one limitation or assumption.
Quick revision
Define the term precisely, show formula substitutions when relevant, and distinguish a change in the variable from a change in its determinants.