how many data points are required to determine a trend within an experimental condition?
63511
We would need more data points to confirm what the trend actually is, if there is a definitive one. So really, two points can create a very rough trend that could be completely wrong, and three points could still do this, but it could also show no trend. So really it depends on the data.
457506
['Measures of central tendency and location (mean, median, mode)', 'Measures of dispersion (range, variance, standard deviation)', 'The extent of symmetry/asymmetry (skewness)', 'The flatness or peakedness (kurtosis).']
533027
The data are at the nominal level of measurement. Such data are not counts or measures of​ anything, so it makes no sense to compute their average​ (mean).
897672
['Estimate the sample mean for the given sample of the population data.', 'Estimate the sample standard deviation for the given data.', 'Dividing the sample standard deviation by the square root of sample mean provides the standard error of the mean (SEM).']
586260
A statistically significant trend is reported if the absolute value of S is greater than the “critical value” of S (obtained from a table). The nonparametric correlation coefficient Kendall's tau (τ) can be calculated to evaluate the nonparametric correlation between two data series.
70880
Two main statistical methods are used in data analysis: descriptive statistics, which summarize data from a sample using indexes such as the mean or standard deviation, and inferential statistics, which draw conclusions from data that are subject to random variation (e.g., observational errors, sampling variation).
1250446
['Find a mean of the set of data.', 'Subtract each number from a mean.', 'Square the result.', 'Add the results together.', 'Divide a result by the total number of numbers in the data set.']
1085497
General Method The same observations are made in both groups over each time period. The data is analyzed by first calculating the difference in first and second time periods, and then subtracting the average gain (or difference) in the control group from the average gain (or difference) in the treatment group.
53508
Also, the prediction interval will not converge to a single value as the sample size increases. You can see this in the formula for the prediction interval: Average t*StDev*1+1n where t is a tabled value from the t distribution which depends on the confidence level and sample size.
808385
With this additional time between tests, three data points are adequate for a trend line. Also, since state assessments are often given in early spring, we felt it was important a trend line was shown as soon as possible so teachers have enough time before the state test to make instructional changes.
541784
['Step 1: Calculate the mean of the data—this is μ in the formula.', 'Step 2: Subtract the mean from each data point. ... ', 'Step 3: Square each deviation to make it positive.', 'Step 4: Add the squared deviations together.', 'Step 5: Divide the sum by the number of data points in the population.']
1226959
['Mean = Sum_of_each_individual/Total_number_of_items.', 'Variance = ((Original_Value – Mean)² + (Original_Value – Mean)² +.... )/(Total_number_of_items - 1)', 'Standard_Deviation = Square_root (Variance)']
550436
Usually, statistical significance is determined by calculating the probability of error (p value) by the t ratio. The difference between two groups (such as an experiment vs. control group) is judged to be statistically significant when p = 0.05 or less.
245669
['Estimating the standard deviation, σ, of the sample data.', 'Multiplying that number by three.', 'Adding (3 x σ to the average) for the UCL and subtracting (3 x σ from the average) for the LCL.']
1400833
['Linearity: The relationship between X and the mean of Y is linear.', 'Homoscedasticity: The variance of residual is the same for any value of X.', 'Independence: Observations are independent of each other.']
971504
Data do's. The number of data points needed in a control chart varies. For variable data used in an X-bar and range (R) chart, a minimum of three to five data points per sample and 20-25 groups of samples is appropriate.
678490
Limitations of Using a Bell Curve In reality, data are not perfectly normal. Sometimes there is skewness - or a lack of symmetry between what falls above and below the mean.