Compute pairwise return correlation between backtests to measure how similarly strategies behave over time.

The diversification score is computed on the mean ABSOLUTE correlation: >= 0.7 → low, >= 0.3 → moderate, otherwise high. A strongly negative correlation (e.g. -0.9) therefore scores as LOW diversification, not high — moving inversely is not independence. Only correlations near 0 read as genuine diversification. Use after running multiple strategy variants to check whether they are real diversifiers or just correlated bets.

Args

• backtest_ids — 2-10 backtest IDs to compare.
• method — pearson (linear) or spearman (rank).

correlate_strategies([id1, id2], method="pearson")

Returns pairwise correlations plus a diversification assessment. Errors if fewer than 2 or more than 10 IDs, any backtest is missing, or equity curves are too short.