To calculate the 95% confidence interval (CI) of LC50 from Probit analysis, follow these steps:

Obtain the LC50: From the probit analysis, get the LC50 value (lethal concentration for 50% of the population).

Standard error (SE) of LC50: Calculate or extract the standard error (SE) of the LC50, typically provided by the probit analysis.

Critical value for 95% CI: Use a z-value of 1.96 for a 95% confidence interval.

Calculate the confidence interval:

Lower bound: LC50−(1.96×SE)LC50 - (1.96 \times SE) Upper bound: LC50+(1.96×SE)LC50 + (1.96 \times SE)

In Excel, you can use the output from your probit analysis (including the LC50 and its SE) to apply these calculations directly in the cells.

Manual calculation of 95% of LC50 using Finney Probit analysis.

Dear Hezam Dhaifallah and Milan B. Arambasic,

First of all, thank you for your suggestion. As Hezem Dhaifallah explained above, based on my figure, the standard error is 0.166656, Z = 1.96, and my LC50 is 7.38 mg/L. This results in a 95% confidence interval (CI) ranging from 7.05 to 7.71 mg/L.

However, when I followed the procedure outlined in the Probit Analysis book on page 32, as provided by Milan B. Arambasic—where the standard error is calculated using the formula SE ≈ ± 1/b√(Snw)—I obtained a range of 4.958 to 9.811 mg/L for the 95% CI.

Since these results differ significantly, I am unsure if I have made an error in my calculations. I have attached my calculations for reference. If anyone could provide guidance on this matter, I would greatly appreciate it.

Best regards,

Send me, please, mortality (nr. mortality/10 animals/concentration) for concentrations: 4, 6, 8 and 10 mg/L. Thank you.

Dear Milan B. Arambasic,

I am sending you my mortality rate data via email, as I was unable to send it through ResearchGate messages. Please find the attachment in this email.

Best regards,