Simpson's Paradox

Simpson's paradox occurs when a trend appears in several groups of data but reverses when the groups are combined. This can lead to misleading conclusions. For example, imagine two hospitals reducing patient mortality rates. Individually, each hospital shows improvement, but when combined data is analyzed, it might look like mortality rates increased. This paradox highlights the importance of considering the context and structure of data before drawing conclusions, as aggregated data can obscure the true relationships within the individual groups.