One assumption of regression analysis is independence of residuals. I checked this assumption and found small autocorrelation (see figure). One remedy would be to incroporate dummy variables for the lags.
But is it always naccessary? Autocorrelation does not affect the estimated coefficients, but the standard errors. The larger the autocorrelation, the larger the impact on standard errors.
Is there a rule of thumb how large the impact would be in my specific case?