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  • LD calculation by logit regression


    I would like to know how I can calculate the LD50, LD90 and LD 95 (lethal dose) for bioassays using logit regression?

    I found probit regression commands, however I would like to apply the formula to STATA programming, please could someone help me?

    1) For LD50 in probit and logit regression the formula is the same:

    local LD50 LD50: exp (-_ b [_cons] / _ b [logdose])

    2) However, for the other LD there is a change:

    I found the links described at the end for the probit model as follows:

    Probit: LDp = (invnormal (p) -constant) / coef

    STATA command:

    local ld90 LD90: exp ((invnorm (0.9) -_ b [_cons]) / _ b [logdose])

    However, for the logit model the formula recommends is:

    Logit: LDp = (log (p / (1-p)) - constant) / coef

    How to program the above command in stata for Logit regression?

    Another question is about normality: If the distribution is not normal, should I calculate LD from the Logit regression? I have read in some places that if the distribution is not parametric, logit regression should be applied for LD.
    Would you have another model suggestion for calculating LD with non-normal distribution?