Extended Data Fig. 6: Small teams cite earlier and less-popular references.

a, We select 1,127,518 WOS articles published in 2010 and find that the probability of observing reference j of age t decreases exponentially with t, such that P(t) ~ e^−λt. For larger teams P(t) decreases faster with t, suggesting that λ is determined by team size m. b, The relationship between m and λ (orange circles) can be fitted as λ ~ m^0.07 (red curve). c, From a and b, we can derive the dependency of E(t), the expected value of t, on m by integrating P(t) from zero to maximum t. This gives E(t) ~ 1/λ ~ m^−0.07. Empirical data (blue rectangles) are consistent with this prediction (red curve). d, Probability of observing reference j with k citations decreases with k, supporting the relationship P(k) ~ k^−α. To control the time window, we include only references published in 2005. For larger teams P(k) decreases more slowly with k, suggesting that α is affected by m. e, The empirical relationship between m and α (purple circles) and the fitting function as α ~ m^−0.05 (red curve). f, From d and e, we can derive the dependency of E(k), the expected value of k, on m by integrating P(k) from minimum to maximum k. This gives E(k) ~ 1 + 1/(α − 2) ~ 1 + 1/(m^−0.05 − 2). The empirical data (green triangles) are consistent with this prediction (red curve).