The Statistical Significance of the Low CMB Mulitipoles

The Wilkinson Microwave Anisotropy Probe (WMAP) has measured lower amplitudes for the temperature quadrupole and octopole anisotropies than expected in the best fitting (concordance) Lambda-dominated cold dark matter cosmology. Some authors have argued that this discrepancy may require new physics. Yet the statistical significance of this result is not clear. Some authors have applied frequentist arguments and claim that the discrepancy would occur by chance about 1 time in 700 if the concordance model is correct. Other authors have used Bayesian arguments to claim that the data show marginal evidence for new physics. I investigate these confusing and apparently conflicting claims using a frequentist analysis and a simplified Bayesian analysis. I conclude that the WMAP results are consistent with the concordance Lambda CDM model.