Effect of variance on the normal distribution curve the area under a normal curve will add to 100%. Generally, if a variable has a higher variance (that is, if a wider spread of values is possible), then the curve will be broader and shorter.Click to see full answer. Then, what is the variance of a normal distribution?The Standard Normal Distribution Table. The standard normal distribution table provides the probability that a normally distributed random variable Z, with mean equal to 0 and variance equal to 1, is less than or equal to z. It does this for positive values of z only (i.e., z-values on the right-hand side of the mean).Subsequently, question is, in which distribution mean and variance are same? For the Poisson distribution the mean and variance are always equal. In other distributions, you can have the mean and variance parameters equal to each other but it may not be necessary for the mean and variance to be equal for all possible distributions with that particular distribution family. Keeping this in consideration, how do you find the variance of a distribution? The variance (σ2), is defined as the sum of the squared distances of each term in the distribution from the mean (μ), divided by the number of terms in the distribution (N). You take the sum of the squares of the terms in the distribution, and divide by the number of terms in the distribution (N).How is variance affected by multiplication?Multiplying a random variable by a constant increases the variance by the square of the constant. The variance of the sum of two or more random variables is equal to the sum of each of their variances only when the random variables are independent.