A meta-analyzed estimate of an effect is:

1

• A meta-analyzed estimate of an effect is
• an average of qualifying study-estimates of the
  effect
• getting the same best units or metric for the
  estimates
• with an inference about its true (large
  study-sample) value
• showing confidence limits and interpreting their
  magnitude
• derived using more weight for study-estimates
  with better precision
• weighting factor is 1/(error variance), when you
  can extract it
• with adjustment for/estimation of effects of
  study characteristics
• effects of design, measurement protocol, mean
  type of subject
• taking into account any clustering of
  study-estimates
• several treatment doses or assay times on same
  subjects
• and taking into account residual differences in
  study-estimates
• the random-effect meta-analysis.