Analyses of public policy regularly express certitude about the consequences of alternative policy choices. Yet policy predictions often are fragile, with conclusions resting on critical unsupported assumptions or leaps of logic. Then the certitude of policy analysis is not credible. I develop a typology of incredible analytical practices and give illustrative cases. I call these practicesconventional certitude, duelling certitudes, conflating science and advocacy, wishful extrapolation,illogical certitude and media overreach.