Different studies used different criteria for the baseline determination and the degree of confirmation (e.g., number of repeat measurements and their timing) for a potential responder. Although the definition of M-protein response varied between studies, the reported response rates showed little variation between the 10 thalidomide studies that report this outcome (Fig. 3). The variation in response rates between the thalidomide studies was not statistically significant (χ2 = 13.5, 9 d.f., P = 0.14) and the mean response rate was 32% (95% CI: 29%, 36%).