Why does a confidence interval including 0 mean the difference is not significant?

Could someone please explain why zero being inside or outside the confidence interval tells you whether or not the difference is significant?

Answer

If the confidence interval (with your chosen level of confidence) includes 0, that implies you think 0 is a reasonable possibility for the true value of the difference. In general, by ‘significant’ people usually mean that they no longer believe the null hypothesis (0) is a reasonable possibility. Note that if a 95% CI doesn’t include 0, the p-value would be <.05, which is the conventional cutoff for 'significance'.

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Source : Link , Question Author : Sara , Answer Author : gung - Reinstate Monica

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