Question about simulated data about spark-analysis

[jakezhusph]

Hi! Thanks for the cool software. I downloaded the example simulated data from processed_data/sim_MOB_pattern2_fc3_tau35_count_power1.csv and when I ran SpatialDE and SPARK on the data, I got 0 (SpatialDE) and 112 (SPARK) significant genes at qval < 0.05. Is this (a single replicate of) the same data used for figure 1c/the expected result? If I understand the plot correctly, it seems that at FDR = 0.05, more genes should be recovered.

Code for spatialDE

counts = pd.read_csv("../SPARK-Analysis/processed_data/sim_MOB_pattern2_fc3_tau35_count_power1.csv", index_col = 0)
counts = counts.T[(counts > 0).sum(0) >= 3].T

x, y = zip(*[pos.split('x') for pos in counts.index])
sample_info = pd.DataFrame({
    'x': np.array(x).astype(float), 
    'y': np.array(y).astype(float), 
    'total_counts': counts.sum(1)
})

norm_expr = NaiveDE.stabilize(counts.T).T
resid_expr = NaiveDE.regress_out(sample_info, norm_expr.T, 'np.log(total_counts)').T

X = sample_info[['x', 'y']]
results = SpatialDE.run(X, resid_expr)

(results.qval < 0.05).sum() # returns 0

Code for SPARK

countdata <- read.csv("../SPARK-Analysis/processed_data/sim_MOB_pattern2_fc3_tau35_count_power1.csv", row.names = 1)

rn <- row.names(countdata)
info <- cbind.data.frame(x = as.numeric(sapply(strsplit(rn, split = "x"), "[", 1)), 
                         y = as.numeric(sapply(strsplit(rn, split = "x"), "[", 2)))
rownames(info) <- row.names(countdata)

spark <- CreateSPARKObject(counts = t(countdata), location = info[,1:2], 
    percentage = 0.1, min_total_counts = 10)
spark@lib_size <- apply(spark@counts, 2, sum)

spark <- spark.vc(spark, covariates = NULL, lib_size = spark@lib_size, 
    num_core = 1, verbose = T, fit.maxiter = 500)
spark <- spark.test(spark, check_positive = T, verbose = T)

spark <- spark.test(spark, check_positive = T, verbose = F)

sum(spark@res_mtest$adjusted_pvalue < 0.05) # returns 102

Hi, this is not the way to calculate the power in the simulation. In the simulation, we know the true signal genes, and therefore we calculate the power directly by counting the number of true signal and false signals among the top genes. The power is essentially the number of true signals detected given certain number of false signals detected. let's say we simulate 1000 genes with 100 signals and 900 non signals. Then you apply both methods to the data, and order the pvalues first, then count how many top genes are signals and how many are non signals. Given detected one false signal, how many true signal you can get, that's the power.

The q-value or the adjusted p values are mainly for the real data, where we don't know the fundamental truth.

Also, the example data is just a toy example, for the detail simulation setting, you can check the supplementary material in our paper.

Let me know if you have any further questions.

[yhtgrace]

Thanks for the clarification!