A Level Psychology OCR Practice Exam

What statistical calculation is key in determining the expected value for Chi-squared?

1. Sum of means for each variable

2. Total cell count minus one

3. Row total multiplied by column total divided by overall total

4. Average score for each group

The correct answer is: Row total multiplied by column total divided by overall total

The expected value for the Chi-squared statistic is determined by the calculation that involves the frequencies in the contingency table. Specifically, the expected frequency for a cell is calculated by taking the row total for that cell, multiplying it by the column total for that cell, and then dividing by the overall total of observations. This method ensures that the expected values reflect the distribution of data under the null hypothesis, which posits that there is no association between the variables being studied. By calculating the expected frequencies this way, researchers can then compare these with the observed frequencies from the data to assess whether the differences are greater than what would be expected by chance. This comparison is central to performing the Chi-squared test and calculating the Chi-squared statistic itself, which informs about the relationship between the variables.