OpenBook Cochran Calculator
OpenBook Cochran Calculator (OC Calculator, 2022) is a free online sample size calculator developed to help research students or other researchers from various fields worldwide, having problem in calculation using Cochran’s Sample Size Formula manually, determine sample size accurately.
Cochran’s Sample Size Formula is written as:
Where:
- n = Number of Samples,
- N = Total Population,
- e = Error Tolerance (Level) or Margin of Error, 0.05,
- p = Sample Proportion, 0.5,
- z = z-value found in Z-score Table, 1.96.
The table below is Z-score Table for most use confidence level or confidence interval.
| Confidence Level | Confidence Interval | Area between zero and z-score | Z-score |
| 90% | 0.10 | 90/2%=0.4500 | 1.65 |
| 95% | 0.05 | 95/2%=0.4750 | 1.96 |
| 99% | 0.01 | 99/2%=0.4950 | 2.58 |
Example Question: Use Cochran’s Sample Size Formula to find out what sample of a population of 17,552,940 people in Lagos State, Nigeria, you need to take for a survey on their Techno Phone preferences.
Step 1: Figure out what you want your confidence level to be. For example, you might want a confidence level of 95 percent (giving you an alpha level or confidence interval or margin error of 0.05).
Step 2. Plug your data into the formula. In this example, we’ll use a 95 percent confidence level with a population size of 17,552,940.
- n = Nz2(p)(1-p)/Ne2 + z2(p)(1-p) =
- 17552940*(1.962)(0.5)(1-0.5)/17552940*(0.052)+(1.962)(0.5)(1-0.5)
= 384.1515925
Step 3: Round your answer to a whole number (because you can’t sample a fraction of a person or thing!)
- 384.1515925 ≅ 384
To use OpenBook Cochran Calculator (OC Calculator, 2022), click here to get it from the homepage.
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