# t-tests and standard deviation excel

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#1
I done a t test on some data but idk what all the values mean. What is variance and df? Also, what does standard deviation, the t test values and the median actually tell you about the data? I have to do a scientific write up on 2 experiments, we were given data sets and we have to do t tests and things and then do the write up and im so confused.
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1 month ago
#2
(Original post by holly0212)
I done a t test on some data but idk what all the values mean. What is variance and df? Also, what does standard deviation, the t test values and the median actually tell you about the data? I have to do a scientific write up on 2 experiments, we were given data sets and we have to do t tests and things and then do the write up and im so confused.
A t-test is a statistical test used to determine whether there is a statistically significant difference in means between two groups. The value you get in a t-test is known as the p-value, the p-value is calculated using the standard deviation of the two groups to work out whether the difference in means is statistically significantly. Statistical significance means that the probability of such a difference between the means is less than can be explained to chance alone. The level of significant is usually set at p=0.05, this means that if your p-value is less than 0.05, then there is less than a 5% chance of such a result arising from chance alone, and so the result is statistically significant.

Presumably in excel when you perform a t-test it calculates variance, standard deviation, df, hence why you have asked? If so, I wouldn’t worry about it too much. Variance is the sum of the square differences from the mean, all divided by the number of data points. What that means is if you have a data set with n data points, first you work out the mean. Then for each data point, you work out the difference from the mean and square this difference. You do this for all data points in the set and divide by the total number of data points. Variance is a measure of spread of the data. Standard deviation is just the square root of the variance.

The median is the value of the middle data point. If you have a data set: 1,2,2,3,6,7,7,8,9.
Here, the middle data point is the 5th value, which is 6, therefore the median is 6. The median is unaffected by extreme values on either side, so is good for skewed data, whereas the mean is affected by extreme values.

As for df, presumably degrees of freedom, I wouldn’t worry about this. It’s essentially the number of data points that are free to vary, which is usually the number of data points in your set minus one.
Last edited by Jpw1097; 1 month ago
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#3
(Original post by Jpw1097)
A t-test is a statistical test used to determine whether there is a statistically significant difference in means between two groups. The value you get in a t-test is known as the p-value, the p-value is calculated using the standard deviation of the two groups to work out whether the difference in means is statistically significantly. Statistical significance means that the probability of such a difference between the means is less than can be explained to chance alone. The level of significant is usually set at p=0.05, this means that if your p-value is less than 0.05, then there is less than a 5% chance of such a result arising from chance alone, and so the result is statistically significant.

Presumably in excel when you perform a t-test it calculates variance, standard deviation, df, hence why you have asked? If so, I wouldn’t worry about it too much. Variance is the sum of the square differences from the mean, all divided by the number of data points. What that means is if you have a data set with n data points, first you work out the mean. Then for each data point, you work out the difference from the mean and square this difference. You do this for all data points in the set and divide by the total number of data points. Variance is a measure of spread of the data. Standard deviation is just the square root of the variance.

The median is the value of the middle data point. If you have a data set: 1,2,2,3,6,7,7,8,9.
Here, the middle data point is the 5th value, which is 6, therefore the median is 6. The median is unaffected by extreme values on either side, so is good for skewed data, whereas the mean is affected by extreme values.

As for df, presumably degrees of freedom, I wouldn’t worry about this. It’s essentially the number of data points that are free to vary, which is usually the number of data points in your set minus one.
Thank you so much!
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