Determining the sample size for a qualitative variable (such as apt or not) will depend on several factors, including the research question, the desired level of precision, and the expected variability in the data. Here are some general steps that you could take to estimate an appropriate sample size:

n = (Z^2 * p * (1-p)) / E^2

Where:

• n = sample size needed
• Z = the Z-value associated with the desired level of confidence (e.g., 1.96 for a 95% confidence interval)
• p = the expected proportion of apt individuals
• E = the desired margin of error

For example, if you expect the proportion of individuals who are apt to be 0.6, and you want a margin of error of ±5 percentage points with a 95% confidence interval, the sample size calculation would be:

n = (1.96^2 * 0.6 * (1-0.6)) / 0.05^2 n = 368

Therefore, you would need a sample size of 368 individuals to achieve the desired level of precision.

It is important to note that these sample size calculations assume a simple random sampling design and certain assumptions about the population distribution. Depending on the research question and study design, different sample size calculations or sampling methods may be more appropriate.