Cell Combining in Chi-squared Test
If any expected frequency is < 5, rows or columns with small expected frequencies should be combined before calculating the chi-squared statistic. The chi-squared test assumes expected frequencies ≥ 5 in all cells.
Real World
A YouGov survey with a small 'No opinion' response category would need that category merged with an adjacent one before running a chi-squared test on political opinion data.
Exam Focus
Always check expected frequencies before calculating χ²; state explicitly which cells were merged and why.
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